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).

openspec/changes/tool-session-progress-and-updates/specs/.pi-map.index.md

@@ -0,0 +1,23 @@
+# specs (index)
+dir: specs
+
+## role
+Contains specification documents and design artifacts that define system requirements, APIs, and behavioral contracts for the project.
+## parent
+index: ./.pi-map.index.md
+map: ./.pi-map.md
+## children
+- specs/session-lifecycle-ux
+  index: specs/session-lifecycle-ux/.pi-map.index.md
+  map: specs/session-lifecycle-ux/.pi-map.md
+- specs/sessions-hub
+  index: specs/sessions-hub/.pi-map.index.md
+  map: specs/sessions-hub/.pi-map.md
+## files
+## links
+index: specs/.pi-map.index.md
+map: specs/.pi-map.md
+## workflows
+-
+## dirty
+-