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/pages/Session.tsx

@@ -38,9 +38,9 @@ export function Session() {
           if (cancelled) return;
           const p = projects.find((x) => x.id === s.project_id);
           if (p) setProject(p);
-        }).catch(() => {});
+        }).catch((err) => console.warn('Session: failed to load project for breadcrumb', err));
       })
-      .catch(() => {});
+      .catch((err) => console.warn('Session: failed to fetch session', err));
     return () => {
       cancelled = true;
     };