feat: implement task management module

Backend (FastAPI):
- Database migration for spaces, projects, task_statuses, tasks tables
- SQLAlchemy models with relationships
- Pydantic schemas for CRUD operations
- Spaces API: CRUD with soft delete
- Projects API: CRUD with auto-created default statuses
- Tasks API: CRUD, status change, assign, subtask support
- Permission middleware with Security Level filtering
- Subtask depth limit (max 2 levels)

Frontend (React + Vite):
- Layout component with navigation
- Spaces list page
- Projects list page
- Tasks list page with status management

Fixes:
- auth_client.py: use 'username' field for external API
- config.py: extend JWT expiry to 7 days
- auth/router.py: sync Redis session with JWT expiry

Tests: 36 passed (unit + integration)
E2E: All APIs verified with real authentication

OpenSpec: add-task-management archived

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/App.tsx

@@ -2,7 +2,11 @@ import { Routes, Route, Navigate } from 'react-router-dom'
 import { useAuth } from './contexts/AuthContext'
 import Login from './pages/Login'
 import Dashboard from './pages/Dashboard'
+import Spaces from './pages/Spaces'
+import Projects from './pages/Projects'
+import Tasks from './pages/Tasks'
 import ProtectedRoute from './components/ProtectedRoute'
+import Layout from './components/Layout'
 
 function App() {
   const { isAuthenticated, loading } = useAuth()
@@ -21,7 +25,39 @@ function App() {
         path="/"
         element={
           <ProtectedRoute>
-            <Dashboard />
+            <Layout>
+              <Dashboard />
+            </Layout>
+          </ProtectedRoute>
+        }
+      />
+      <Route
+        path="/spaces"
+        element={
+          <ProtectedRoute>
+            <Layout>
+              <Spaces />
+            </Layout>
+          </ProtectedRoute>
+        }
+      />
+      <Route
+        path="/spaces/:spaceId"
+        element={
+          <ProtectedRoute>
+            <Layout>
+              <Projects />
+            </Layout>
+          </ProtectedRoute>
+        }
+      />
+      <Route
+        path="/projects/:projectId"
+        element={
+          <ProtectedRoute>
+            <Layout>
+              <Tasks />
+            </Layout>
           </ProtectedRoute>
         }
       />