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/routes/dashboards.ts

@@ -42,6 +42,7 @@ export function createDashboardsRouter(db: Db): Hono {
     const [dashboard] = await db.insert(dashboards).values({
       name,
       description: body.description ?? null,
+      team_id: body.team_id || null,
       layout: body.layout ?? [],
       is_default: body.is_default ?? false,
     }).returning();
@@ -87,9 +88,9 @@ export function createDashboardsRouter(db: Db): Hono {
     if (body.name !== undefined) updateData.name = String(body.name).trim();
     if (body.description !== undefined) updateData.description = body.description ?? null;
     if (body.layout !== undefined) updateData.layout = body.layout;
+    if (body.team_id !== undefined) updateData.team_id = body.team_id || null;
     if (body.is_default !== undefined) {
       updateData.is_default = body.is_default;
-      // If setting this as default, unset others
       if (body.is_default) {
         await db.update(dashboards)
           .set({ is_default: false })