feat: add dashboards — tables, CRUD API, widget data endpoint

- New dashboards table (name, description, layout, is_default)
- New dashboard_widgets table (view_id, title, widget_type, position, config)
- GET/POST/PATCH/DELETE /dashboards
- GET/POST/PATCH/DELETE /dashboards/:id/widgets
- GET /dashboards/:id/widgets/:id/data — runs saved view filters,
  returns pre-aggregated data for count/ticket_list/status_chart/grouped_counts
- is_default uniqueness enforced on PATCH

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

drizzle/migrations/meta/_journal.json

@@ -29,6 +29,13 @@
       "when": 1780995910694,
       "tag": "0003_dry_caretaker",
       "breakpoints": true
+    },
+    {
+      "idx": 4,
+      "version": "7",
+      "when": 1780996807814,
+      "tag": "0004_sturdy_natasha_romanoff",
+      "breakpoints": true
     }
   ]
 }