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)/new-contact.tsx

@@ -64,16 +64,17 @@ export default function NewContactScreen() {
         if (!addr) { setError(`@${name} is not registered on this chain`); return; }
         address = addr;
       }
-      // Block self-lookup — can't message yourself, and the on-chain
-      // CONTACT_REQUEST tx would go through but serve no purpose.
+      // Self-lookup: skip the contact-request dance entirely and jump straight
+      // to Saved Messages (self-chat). No CONTACT_REQUEST tx is needed — the
+      // chat-with-self flow is purely local storage.
       if (keyFile && address.toLowerCase() === keyFile.pub_key.toLowerCase()) {
-        setError("That's you. You can't send a contact request to yourself.");
+        router.replace(`/(app)/chats/${keyFile.pub_key}` as never);
         return;
       }
       const identity = await getIdentity(address);
       const resolvedAddr = identity?.pub_key ?? address;
       if (keyFile && resolvedAddr.toLowerCase() === keyFile.pub_key.toLowerCase()) {
-        setError("That's you. You can't send a contact request to yourself.");
+        router.replace(`/(app)/chats/${keyFile.pub_key}` as never);
         return;
       }
       setResolved({