Add Dashboards UI: PromQL-backed bar/line/pie panels saved per profile (ticket 014)

Backend: replace Profile.dashboards' opaque JSON stub with typed
Dashboard/Panel structs, add ProfileStore CRUD (create/save/list/delete
dashboard) and matching /api/settings/profiles/:name/dashboards[/:id] routes,
with tests covering the HTTP round trip and persistence across a simulated
restart.

Frontend: add recharts (lightweight, React 19-compatible) and a Dashboards
component with a dashboard builder (create dashboards, add/remove/edit panels
with a PromQL query + chart type), live per-panel previews that respect the
active time range and show malformed-query errors inline instead of crashing,
and load/save wired to the new profile-backed persistence.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o

webapp/package.json

@@ -13,6 +13,7 @@
     "@tailwindcss/vite": "^4.3.3",
     "react": "^19.2.8",
     "react-dom": "^19.2.8",
+    "recharts": "^3.10.1",
     "tailwindcss": "^4.3.3"
   },
   "devDependencies": {