feat(plot): Chunk #5 story whiteboard, timeline & plot beats

Story whiteboard built on React Flow v11: free-form canvas of typed
nodes (character, world, chapter, note, image, group) with draggable
leads-to/contrasts/causes edges, cross-link selectors (chapter/entity),
linked-node badges, and an "Add beats to board" import from the plot.

Plot beats feature set:
- Status/locking (draft/revised/locked) with a progress bar
- Beat templates (three-act, save-the-cat, seven-point, custom)
- Timeline route with search/chapter/character filters
- Entity cross-links (entityIds) on beats and board nodes
- getBoard added to the StorageAdapter contract (local + server) and
  REST endpoints; loadBoard now restores persisted board state

Storage & server:
- PlotBeat type (status, entityIds) across core types, Dexie schema,
  and server mapping/routes/migration (002_plot_beats.sql)
- SQLite-safe column names (beat_order, entity_ids)
- Server seed data for plot beats

UI: accent Button variant, Badge variants, plot/timeline/whiteboard
stylesheets. Tests: templates module, plot-beat store round-trip,
board getBoard. typecheck, lint, test, and build all green.

apps/web/package.json

@@ -18,16 +18,17 @@
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
     "react-router-dom": "^7.1.1",
+    "reactflow": "^11",
     "zustand": "^5.0.2"
   },
   "devDependencies": {
+    "@types/node": "^22.10.2",
     "@types/react": "^19.0.2",
     "@types/react-dom": "^19.0.2",
     "@vitejs/plugin-react": "^4.3.4",
     "jsdom": "^25.0.1",
     "typescript": "^5.7.2",
     "vite": "^6.0.3",
-    "vitest": "^2.1.8",
-    "@types/node": "^22.10.2"
+    "vitest": "^2.1.8"
   }
 }