feat: implement tool-session progress panel and live list updates

- Add SessionOperationsContext + SessionProgressPanel for global,
  non-blocking lifecycle progress (create/start/stop/restart/delete/
  recreate-tunnel) driven by SSE events.
- Promote SessionsContext to authoritative shared session state with
  refresh, addOrUpdateSession, and removeSession helpers.
- Wire AppShell, DashboardPage, SessionsPage, useInstanceActions,
  ToolStarter, and InstanceList into shared state so lists update
  immediately after create/delete without manual refresh.
- Remove legacy blocking overlays from CreateSessionForm, SessionCard,
  and InstanceList; keep disabled states and inline spinners only.
- Update DashboardPage tests to wrap with SessionsProvider and
  SessionOperationsProvider.
- Add .cache/ to .gitignore.

Quality gates: npm run typecheck, npm run lint, npm test -- --run
(82 passed).

.gitignore

@@ -55,3 +55,4 @@ Thumbs.db
 .sisyphus/
 .pi-lens/
 minerv3/
+.cache/