feat: add teams/groups with dashboard scoping

Schema:
- teams table (name unique, description)
- team_members table (team_id, user_id, unique constraint)
- team_id column on dashboards

API:
- GET/POST/PATCH/DELETE /teams
- POST /teams/:id/members (add user)
- DELETE /teams/:id/members/:userId (remove user)
- dashboards support team_id on create/update

Frontend:
- Teams tab in admin: CRUD + member management with add/remove
- Sidebar: dashboards filtered to user's teams
  (unassigned dashboards visible to all)
- Compact dashboard picker dropdown in sidebar

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/index.ts

@@ -14,6 +14,7 @@ import { createUsersRouter } from './routes/users.ts';
 import { createTemplatesRouter } from './routes/templates.ts';
 import { createViewsRouter } from './routes/views.ts';
 import { createDashboardsRouter } from './routes/dashboards.ts';
+import { createTeamsRouter } from './routes/teams.ts';
 
 let db: Db | null = null;
 
@@ -39,6 +40,7 @@ app.route('/users', createUsersRouter(getDb()));
 app.route('/templates', createTemplatesRouter(getDb()));
 app.route('/views', createViewsRouter(getDb()));
 app.route('/dashboards', createDashboardsRouter(getDb()));
+app.route('/teams', createTeamsRouter(getDb()));
 
 export default app;
 export { app };