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/server/src/services/file_index.ts

@@ -33,6 +33,7 @@ async function snapMtimes(root: string): Promise<MtimeSnap> {
   const rootStat = await fs.stat(root);
   let gitHead: number | null = null;
   let gitIndex: number | null = null;
+  // best-effort; ignore failure because the project may not be a git repo
   try { gitHead = (await fs.stat(path.join(root, '.git', 'HEAD'))).mtimeMs; } catch {}
   try { gitIndex = (await fs.stat(path.join(root, '.git', 'index'))).mtimeMs; } catch {}
   return { root: rootStat.mtimeMs, gitHead, gitIndex };