chore: surface swallowed errors + remove dead session_renamed paths

Swallowed-error logging (audit Feature 3):
- file_index.ts:36-37 (git mtime probes): comment — best-effort, project
  may not be a git repo.
- useUserEvents.ts:44 / 53 (ws.close on error / unmount): comments —
  best-effort, socket may already be closing.
- RightRail.tsx:38 (localStorage write): comment — best-effort, quota or
  private mode.
- App.tsx:21 (api.sessions.get for RightRail projectId): replaced silent
  catch with console.warn.
- Session.tsx:38, 41 (session fetch + project list for breadcrumb):
  replaced silent catches with console.warn.

H1: ProjectSidebar.tsx:189 — dropped the local sessionEvents.emit
({type:'session_renamed'}) after PATCH. Server publishes via
broker.publishUser since v1.4; useUserEvents forwards.

H2: useSessionStream.ts session_renamed case removed (dead — no
server code path publishes session_renamed on the per-session WS
channel; only user channel via broker.publishUser). Also dropped the
session_renamed variant from WsFrame (in apps/web/src/api/types.ts)
to keep the discriminated-union switch exhaustive.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/hooks/useUserEvents.ts

@@ -40,7 +40,8 @@ export function useUserEvents(): void {
       };
 
       ws.onerror = () => {
-        // close handler will trigger reconnect
+        // close handler will trigger reconnect; best-effort, ignore failure
+        // because the socket may already be closing
         try { ws?.close(); } catch {}
       };
     };
@@ -50,6 +51,7 @@ export function useUserEvents(): void {
     return () => {
       unmounted = true;
       if (reconnectTimer) clearTimeout(reconnectTimer);
+      // best-effort cleanup; ignore failure because the socket may already be closed
       if (ws) try { ws.close(); } catch {}
     };
   }, []);