feat: workspace frontend core (PR-3)

- Workspace types, API client, hooks (useWorkspaces, useWorkspaceActions)
- WorkspaceCard, WorkspaceCreateForm, StartToolModal components
- WorkspacesPage with list, create, sync, delete, start-tool flow
- Sidebar navigation: new 'Workspaces' entry
- Router: /workspaces route
- TypeScript + eslint clean

apps/web/src/router.tsx

@@ -16,6 +16,7 @@ import { ToolWorkshopPage } from "./pages/tool-workshop";
 import { SSHKeysPage } from "./pages/ssh-keys";
 import { ConfigProfilesPage } from "./pages/config-profiles";
 import { SessionsPage } from "./pages/sessions";
+import { WorkspacesPage } from "./pages/workspaces";
 
 export const AppRouter = () => {
   return (
@@ -45,6 +46,7 @@ export const AppRouter = () => {
           <Route path="*" element={<Navigate to="general" replace />} />
         </Route>
         <Route path="sessions" element={<SessionsPage />} />
+        <Route path="workspaces" element={<WorkspacesPage />} />
         <Route path="tool-workshop" element={<ToolWorkshopPage />} />
         <Route path="instances/:instanceId/terminal" element={<TerminalPage />} />
       </Route>