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/components/ChatTile.tsx

@@ -57,10 +57,12 @@ export interface ChatTileProps {
   contact:     Contact;
   lastMessage: Message | null;
   onPress:     () => void;
+  /** Render as the Saved Messages tile (blue bookmark avatar, fixed name). */
+  saved?:      boolean;
 }
 
-export function ChatTile({ contact: c, lastMessage, onPress }: ChatTileProps) {
-  const name = displayName(c);
+export function ChatTile({ contact: c, lastMessage, onPress, saved }: ChatTileProps) {
+  const name = saved ? 'Saved Messages' : displayName(c);
   const last = lastMessage;
 
   // Визуальный маркер типа чата.
@@ -92,7 +94,8 @@ export function ChatTile({ contact: c, lastMessage, onPress }: ChatTileProps) {
           name={name}
           address={c.address}
           size={44}
-          dotColor={c.x25519Pub && (!c.kind || c.kind === 'direct') ? '#3ba55d' : undefined}
+          saved={saved}
+          dotColor={!saved && c.x25519Pub && (!c.kind || c.kind === 'direct') ? '#3ba55d' : undefined}
         />
 
         <View style={{ flex: 1, marginLeft: 12, minWidth: 0 }}>
@@ -143,9 +146,11 @@ export function ChatTile({ contact: c, lastMessage, onPress }: ChatTileProps) {
             >
               {last
                 ? lastPreview(last)
-                : c.x25519Pub
-                  ? 'Tap to start encrypted chat'
-                  : 'Waiting for identity…'}
+                : saved
+                  ? 'Your personal notes & files'
+                  : c.x25519Pub
+                    ? 'Tap to start encrypted chat'
+                    : 'Waiting for identity…'}
             </Text>
 
             {unread !== null && (