feat: session management fixes and sessions hub

- Add confirmation dialogs for stop/delete on dashboard
- Filter deleted sessions immediately without reload
- Add tunnel health polling with error badges
- Add Sessions nav item with active count badge
- Route /sessions to SessionsPage component

Quality gates: 43/43 tests pass, typecheck pass, lint pass

Refs: openspec/changes/session-management-fixes
Refs: openspec/changes/sessions-hub

apps/web/src/router.tsx

@@ -16,12 +16,12 @@ import { ToolWorkshopPage } from "./pages/tool-workshop";
 import { SSHKeysPage } from "./pages/ssh-keys";
 import { ToolConfigsPage } from "./pages/tool-configs";
 import { ToolTypesPage } from "./pages/tool-types";
+import { SessionsPage } from "./pages/sessions";
 
 export const AppRouter = () => {
   return (
     <Routes>
       <Route path="/login" element={<LoginRedirectPage />} />
-      <Route path="/sessions" element={<Navigate to="/" replace />} />
       <Route path="/ssh-keys" element={<Navigate to="/settings/ssh-keys" replace />} />
       <Route path="/tool-types" element={<Navigate to="/settings/tool-types" replace />} />
       <Route path="/tool-configs" element={<Navigate to="/settings/tool-configs" replace />} />
@@ -48,6 +48,7 @@ export const AppRouter = () => {
           <Route path="tool-configs" element={<ToolConfigsPage />} />
           <Route path="*" element={<Navigate to="general" replace />} />
         </Route>
+        <Route path="sessions" element={<SessionsPage />} />
         <Route path="tool-workshop" element={<ToolWorkshopPage />} />
         <Route path="instances/:instanceId/terminal" element={<TerminalPage />} />
       </Route>