fix: recover chat replies and organize setup navigation [skip ci]

Targeted source-only patch from reviewed local e370485. Adds bounded realtime/catch-up recovery and moves the setup wizard under System. Static checks only; regression tests, full build and runtime verification have not been run. No deployment. Separate hardening-review branch is not merged. Expected tree: 6235478b9a.

docs/fixes/chat-realtime-recovery.md

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+# Support chat realtime recovery
+
+This targeted change is based on canonical Gitea main snapshot
+`e57610a27c556e005b9b3b68115477ba1fdd3f1b` (tree
+`9cf938c2498ce6b63faaad7cf8b286c1cfe7a5ef`). It does not import the separate
+hardening-review branch.
+
+## Report and source findings
+
+The reported scenario is opening a new chat from a previous one: sending works,
+but replies appear only after a page reload. Source inspection does **not** prove
+why the deployed WebSocket fails. The deployed version, reverse proxy, browser
+handshake and network have not been observed or tested for this report.
+
+The source does establish these recovery gaps:
+
+- A socket in `CONNECTING` has no deadline; subsequent create/select/send paths
+  see it and return without starting a replacement.
+- HTTP fallback checks end after 1.5, 3.5 and 7 seconds, so a later reply is not
+  retrieved while realtime remains unavailable.
+- Reusing an open socket on create/select bypasses the shared status repair path.
+- Initial history failure prevents bootstrap/retry from starting realtime.
+- A replaced socket's late close can clear the current heartbeat/subscription
+  bookkeeping. A late close-conversation response can affect a newer selection.
+
+## Changes
+
+- Bound connection/authentication attempts to 15 seconds, invalidate abandoned
+  attempts, and retry using the existing exponential reconnect policy.
+- Ignore close events from replaced sockets before touching current state.
+- Route new/selected chats through the existing subscription/connection helper.
+- Fetch late replies every 5 seconds only while the chat is open, visible, has
+  an active nonclosed conversation, and realtime is not connected. Never label
+  HTTP fallback as an online WebSocket.
+- Keep latest-message refresh single-flight with a 15-second abort deadline.
+  Cancel previous-view requests and fence their completion before starting a new
+  one. Ignore stale identity/view results, stop recovery on connection, hiding,
+  close or teardown, and recover on focus, visibility or network return.
+  Background recovery failures remain quiet. The optional API AbortSignal is
+  backward-compatible with existing history/pagination callers.
+- Connect independently of initial HTTP history success and merge history so it
+  cannot remove a reply already delivered by realtime.
+- Restrict a close response to the conversation it actually closed.
+
+No backend, SDK bundle, credentials, database, deployment configuration or
+production data is changed.
+
+## Validation status
+
+Completed static checks only:
+
+- `git diff --check`.
+- Isolated strict TypeScript compile of `web/lib/realtime-connection.ts` using an
+  already installed TypeScript 6.0.3 compiler.
+- TypeScript syntax/transpile diagnostics for the four changed production files.
+- JavaScript syntax checks for the two focused regression files.
+
+Added offline mock regressions for delayed replies beyond seven seconds, moving
+from a previous chat, resubscription, stuck handshakes, late authentication and
+socket close events, hidden/unmounted lifecycle, single-flight fallback,
+identity/view changes, abort deadlines, stalled previous-view fetches, history
+failures and late close responses.
+
+**The regression tests have not been executed.** Full project typecheck, lint,
+build and browser/runtime validation have not been run; permission for tests,
+installation and runtime verification remains pending. No services were started,
+real support messages sent, or deployment performed. Do not describe this source
+patch as a verified production fix.