feat: resource caps, Saved Messages, author walls, docs for node bring-up

Node flags (cmd/node/main.go):
  --max-cpu / --max-ram-mb — Go runtime caps (GOMAXPROCS / GOMEMLIMIT)
  --feed-disk-limit-mb — hard 507 refusal for new post bodies over quota
  --chain-disk-limit-mb — advisory watcher (can't reject blocks without
  breaking consensus; logs WARN every minute)

Client — Saved Messages (self-chat):
  - Auto-created on sign-in, pinned top of chat list, blue bookmark avatar
  - Send short-circuits the relay (no encrypt, no fee, no mailbox hop)
  - Empty state rendered outside inverted FlatList — fixes the mirrored
    "say hi…" on Android RTL-aware layout builds
  - PostCard shows "You" for own posts instead of the self-contact alias

Client — user walls:
  - New route /(app)/feed/author/[pub] with infinite-scroll via
    `created_at` cursor and pull-to-refresh
  - Profile screen gains "View posts" button (universal) next to
    "Open chat" (contact-only)

Feed pipeline:
  - Bump client JPEG quality 0.5 → 0.75 to match server scrubber (Q=75),
    so a 60 KiB compose doesn't balloon past 256 KiB after server re-encode
  - ErrPostTooLarge now wraps with the actual size vs cap, errors.Is
    preserved in the HTTP layer
  - FeedMailbox quota + DiskUsage surface — supports new CLI flag

README:
  - Step-by-step "first node / joiner" section on the landing page,
    full flag tables incl. the new resource-cap group, minimal
    checklists for open/private/low-end deployments

client-app/app/(app)/profile/[address].tsx

@@ -13,7 +13,7 @@
  *   push stack, so tapping Back returns the user to whatever screen
  *   pushed them here (feed card tap, chat header tap, etc.).
  */
-import React, { useState } from 'react';
+import React, { useEffect, useState } from 'react';
 import {
   View, Text, ScrollView, Pressable, ActivityIndicator,
 } from 'react-native';
@@ -27,8 +27,11 @@ import { Avatar } from '@/components/Avatar';
 import { Header } from '@/components/Header';
 import { IconButton } from '@/components/IconButton';
 import { followUser, unfollowUser } from '@/lib/feed';
-import { humanizeTxError } from '@/lib/api';
-import { safeBack } from '@/lib/utils';
+import {
+  humanizeTxError, getBalance, getIdentity, getRelayFor,
+  type IdentityInfo, type RegisteredRelayInfo,
+} from '@/lib/api';
+import { safeBack, formatAmount } from '@/lib/utils';
 
 function shortAddr(a: string, n = 10): string {
   if (!a) return '—';
@@ -46,10 +49,35 @@ export default function ProfileScreen() {
   const [followingBusy, setFollowingBusy] = useState(false);
   const [copied, setCopied]             = useState(false);
 
+  // On-chain enrichment — fetched once per address mount.
+  const [balanceUT, setBalanceUT] = useState<number | null>(null);
+  const [identity, setIdentity]   = useState<IdentityInfo | null>(null);
+  const [relay, setRelay]         = useState<RegisteredRelayInfo | null>(null);
+  const [loadingChain, setLoadingChain] = useState(true);
+
   const isMe = !!keyFile && keyFile.pub_key === address;
-  const displayName = contact?.username
-    ? `@${contact.username}`
-    : contact?.alias ?? (isMe ? 'You' : shortAddr(address ?? '', 6));
+
+  useEffect(() => {
+    if (!address) return;
+    let cancelled = false;
+    setLoadingChain(true);
+    Promise.all([
+      getBalance(address).catch(() => 0),
+      getIdentity(address).catch(() => null),
+      getRelayFor(address).catch(() => null),
+    ]).then(([bal, id, rel]) => {
+      if (cancelled) return;
+      setBalanceUT(bal);
+      setIdentity(id);
+      setRelay(rel);
+    }).finally(() => { if (!cancelled) setLoadingChain(false); });
+    return () => { cancelled = true; };
+  }, [address]);
+  const displayName = isMe
+    ? 'Saved Messages'
+    : contact?.username
+      ? `@${contact.username}`
+      : contact?.alias ?? shortAddr(address ?? '', 6);
 
   const copyAddress = async () => {
     if (!address) return;
@@ -94,7 +122,7 @@ export default function ProfileScreen() {
       <ScrollView contentContainerStyle={{ padding: 14, paddingBottom: insets.bottom + 30 }}>
         {/* ── Hero: avatar + Follow button ──────────────────────────── */}
         <View style={{ flexDirection: 'row', alignItems: 'flex-end', marginBottom: 12 }}>
-          <Avatar name={displayName} address={address} size={72} />
+          <Avatar name={displayName} address={address} size={72} saved={isMe} />
           <View style={{ flex: 1 }} />
           {!isMe ? (
             <Pressable
@@ -131,16 +159,18 @@ export default function ProfileScreen() {
             </Pressable>
           ) : (
             <Pressable
-              onPress={() => router.push('/(app)/settings' as never)}
+              onPress={() => keyFile && router.push(`/(app)/chats/${keyFile.pub_key}` as never)}
               style={({ pressed }) => ({
-                paddingHorizontal: 18, paddingVertical: 9,
+                paddingHorizontal: 16, paddingVertical: 9,
                 borderRadius: 999,
+                flexDirection: 'row', alignItems: 'center', gap: 6,
                 backgroundColor: pressed ? '#1a1a1a' : '#111111',
                 borderWidth: 1, borderColor: '#1f1f1f',
               })}
             >
+              <Ionicons name="bookmark" size={13} color="#f0b35a" />
               <Text style={{ color: '#ffffff', fontWeight: '700', fontSize: 13 }}>
-                Edit
+                Saved Messages
               </Text>
             </Pressable>
           )}
@@ -159,13 +189,14 @@ export default function ProfileScreen() {
           )}
         </View>
 
-        {/* Open chat — single CTA, full width, icon inline with text.
-            Only when we know this is a contact (direct chat exists). */}
-        {!isMe && contact && (
+        {/* Action row — View posts is universal (anyone can have a wall,
+            even non-contacts). Open chat appears alongside only when this
+            address is already a direct-chat contact. */}
+        <View style={{ flexDirection: 'row', gap: 8, marginTop: 14 }}>
           <Pressable
-            onPress={openChat}
+            onPress={() => address && router.push(`/(app)/feed/author/${address}` as never)}
             style={({ pressed }) => ({
-              marginTop: 14,
+              flex: 1,
               flexDirection: 'row',
               alignItems: 'center',
               justifyContent: 'center',
@@ -176,12 +207,34 @@ export default function ProfileScreen() {
               borderWidth: 1, borderColor: '#1f1f1f',
             })}
           >
-            <Ionicons name="chatbubble-outline" size={15} color="#ffffff" />
+            <Ionicons name="document-text-outline" size={15} color="#ffffff" />
             <Text style={{ color: '#ffffff', fontWeight: '600', fontSize: 14 }}>
-              Open chat
+              View posts
             </Text>
           </Pressable>
-        )}
+
+          {!isMe && contact && (
+            <Pressable
+              onPress={openChat}
+              style={({ pressed }) => ({
+                flex: 1,
+                flexDirection: 'row',
+                alignItems: 'center',
+                justifyContent: 'center',
+                gap: 6,
+                paddingVertical: 11,
+                borderRadius: 999,
+                backgroundColor: pressed ? '#1a1a1a' : '#111111',
+                borderWidth: 1, borderColor: '#1f1f1f',
+              })}
+            >
+              <Ionicons name="chatbubble-outline" size={15} color="#ffffff" />
+              <Text style={{ color: '#ffffff', fontWeight: '600', fontSize: 14 }}>
+                Open chat
+              </Text>
+            </Pressable>
+          )}
+        </View>
 
         {/* ── Info card ───────────────────────────────────────────────── */}
         <View
@@ -225,6 +278,63 @@ export default function ProfileScreen() {
             />
           </Pressable>
 
+          {/* Username — shown if the on-chain identity record has one.
+              Different from contact.username (which may be a local alias). */}
+          {identity?.nickname ? (
+            <>
+              <Divider />
+              <InfoRow
+                label="Username"
+                value={`@${identity.nickname}`}
+                icon="at-outline"
+              />
+            </>
+          ) : null}
+
+          {/* DC address — the human-readable form of the pub key. */}
+          {identity?.address ? (
+            <>
+              <Divider />
+              <InfoRow
+                label="DC address"
+                value={identity.address}
+                icon="pricetag-outline"
+              />
+            </>
+          ) : null}
+
+          {/* Balance — always shown once fetched. */}
+          <Divider />
+          <InfoRow
+            label="Balance"
+            value={loadingChain
+              ? '…'
+              : `${formatAmount(balanceUT ?? 0)} UT`}
+            icon="wallet-outline"
+          />
+
+          {/* Relay node — shown only if this address is a registered relay. */}
+          {relay && (
+            <>
+              <Divider />
+              <InfoRow
+                label="Relay node"
+                value={`${formatAmount(relay.relay.fee_per_msg_ut)} UT / msg`}
+                icon="radio-outline"
+              />
+              {relay.last_heartbeat ? (
+                <>
+                  <Divider />
+                  <InfoRow
+                    label="Last seen"
+                    value={new Date(relay.last_heartbeat * 1000).toLocaleString()}
+                    icon="pulse-outline"
+                  />
+                </>
+              ) : null}
+            </>
+          )}
+
           {/* Encryption status */}
           {contact && (
             <>