Add multi-tenancy with Teams feature

Implement team-based organization for projects with role-based access control:

Backend:
- Add teams and team_memberships database tables (migrations 009, 009b)
- Add Team and TeamMembership ORM models with relationships
- Implement TeamAuthorizationService for team-level access control
- Add team CRUD, membership, and projects API endpoints
- Update project creation to support team assignment

Frontend:
- Add TeamContext for managing team state with localStorage persistence
- Add TeamSelector component for switching between teams
- Add TeamsPage, TeamDashboardPage, TeamSettingsPage, TeamMembersPage
- Add team API client functions
- Update navigation with Teams link

Security:
- Team role hierarchy: owner > admin > member
- Membership checked before system admin fallback
- Self-modification prevention for role changes
- Email visibility restricted to team admins/owners
- Slug validation rejects consecutive hyphens

Tests:
- Unit tests for TeamAuthorizationService
- Integration tests for all team API endpoints

frontend/src/App.tsx

@@ -1,5 +1,6 @@
 import { Routes, Route, Navigate, useLocation } from 'react-router-dom';
 import { AuthProvider, useAuth } from './contexts/AuthContext';
+import { TeamProvider } from './contexts/TeamContext';
 import Layout from './components/Layout';
 import Home from './pages/Home';
 import ProjectPage from './pages/ProjectPage';
@@ -11,6 +12,10 @@ import APIKeysPage from './pages/APIKeysPage';
 import AdminUsersPage from './pages/AdminUsersPage';
 import AdminOIDCPage from './pages/AdminOIDCPage';
 import ProjectSettingsPage from './pages/ProjectSettingsPage';
+import TeamsPage from './pages/TeamsPage';
+import TeamDashboardPage from './pages/TeamDashboardPage';
+import TeamSettingsPage from './pages/TeamSettingsPage';
+import TeamMembersPage from './pages/TeamMembersPage';
 
 // Component that checks if user must change password
 function RequirePasswordChange({ children }: { children: React.ReactNode }) {
@@ -45,6 +50,10 @@ function AppRoutes() {
                 <Route path="/settings/api-keys" element={<APIKeysPage />} />
                 <Route path="/admin/users" element={<AdminUsersPage />} />
                 <Route path="/admin/oidc" element={<AdminOIDCPage />} />
+                <Route path="/teams" element={<TeamsPage />} />
+                <Route path="/teams/:slug" element={<TeamDashboardPage />} />
+                <Route path="/teams/:slug/settings" element={<TeamSettingsPage />} />
+                <Route path="/teams/:slug/members" element={<TeamMembersPage />} />
                 <Route path="/project/:projectName" element={<ProjectPage />} />
                 <Route path="/project/:projectName/settings" element={<ProjectSettingsPage />} />
                 <Route path="/project/:projectName/:packageName" element={<PackagePage />} />
@@ -60,7 +69,9 @@ function AppRoutes() {
 function App() {
   return (
     <AuthProvider>
-      <AppRoutes />
+      <TeamProvider>
+        <AppRoutes />
+      </TeamProvider>
     </AuthProvider>
   );
 }