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>

drizzle/migrations/meta/_journal.json

@@ -36,6 +36,13 @@
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+    },
+    {
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+      "tag": "0005_spotty_leader",
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 }