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/src/App.tsx

@@ -5,6 +5,7 @@ import { ToastViewport } from "@pubscript/ui";
 import Write from "./routes/Write.js";
 import { Characters } from "./routes/Characters.js";
 import { Plot } from "./routes/Plot.js";
+import { Timeline } from "./routes/Timeline.js";
 import { Whiteboard } from "./routes/Whiteboard.js";
 import { AI } from "./routes/AI.js";
 import { Projects } from "./routes/Projects.js";
@@ -15,6 +16,7 @@ const NAV = [
   { to: "/", label: "Write", icon: "✎", end: true },
   { to: "/characters", label: "Entities", icon: "👥", end: false },
   { to: "/plot", label: "Plot", icon: "🗺", end: false },
+  { to: "/timeline", label: "Timeline", icon: "📅", end: false },
   { to: "/whiteboard", label: "Whiteboard", icon: "🧩", end: false },
   { to: "/ai", label: "AI", icon: "✨", end: false },
   { to: "/projects", label: "Projects", icon: "📁", end: false },
@@ -45,6 +47,7 @@ export default function App() {
           <Route path="/" element={<Write />} />
           <Route path="/characters" element={<Characters />} />
           <Route path="/plot" element={<Plot />} />
+          <Route path="/timeline" element={<Timeline />} />
           <Route path="/whiteboard" element={<Whiteboard />} />
           <Route path="/ai" element={<AI />} />
           <Route path="/projects" element={<Projects />} />