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.

server/src/mapping.ts

@@ -7,6 +7,7 @@ import type {
   Character,
   Entity,
   Note,
+  PlotBeat,
   Project,
   ProjectMeta,
   User,
@@ -69,6 +70,21 @@ export interface BoardRow {
   edges: string;
   updated_at: string;
 }
+
+export interface PlotBeatRow {
+  id: string;
+  project_id: string;
+  title: string;
+  body: string;
+  act: number;
+  type: string;
+  beat_order: number;
+  status: string;
+  chapter_id: string | null;
+  entity_ids: string;
+  created_at: string;
+  updated_at: string;
+}
 export interface AISessionRow {
   id: string;
   project_id: string;
@@ -160,6 +176,34 @@ export function toBoard(r: BoardRow): Board {
   };
 }
 
+export function toPlotBeat(r: PlotBeatRow): PlotBeat {
+  return {
+    id: r.id,
+    projectId: r.project_id,
+    title: r.title,
+    body: r.body,
+    act: r.act,
+    type: r.type as PlotBeat["type"],
+    order: r.beat_order,
+    status: (r.status as PlotBeat["status"]) ?? "draft",
+    chapterId: r.chapter_id ?? undefined,
+    entityIds: parseEntityIds(r.entity_ids),
+    createdAt: r.created_at,
+    updatedAt: r.updated_at,
+  };
+}
+
+/** Parse the JSON `entity_ids` column into a string[] (empty when blank). */
+function parseEntityIds(raw: string): string[] {
+  if (!raw) return [];
+  try {
+    const parsed = JSON.parse(raw);
+    return Array.isArray(parsed) ? parsed.filter((id): id is string => typeof id === "string") : [];
+  } catch {
+    return [];
+  }
+}
+
 export function toAISession(r: AISessionRow): AISession {
   return {
     id: r.id,