feat(dashboard): merge Analytics into Dashboard, remove Kanban Board

Closes issue #5 (Dashboard | Update menu & page):
- Analytics content (heatmap, sparkline, token/cost/workflow/productivity
  charts) moves into a new "Analytics" tab on the Dashboard page, alongside
  the existing Monitor/Health tabs. The standalone Analytics page, its
  /analytics route, and its sidebar menu entry are removed.
- The Kanban Board page, its /kanban route, and its sidebar menu entry are
  removed entirely (page content deleted, not just hidden).
- Updated ARCHITECTURE.md, README.md, client/README.md, docs/API.md, and
  the affected client tests/snapshots to match.

client/src/App.tsx

@@ -39,11 +39,9 @@
  * - `./components/Layout`
  * - `./components/SplashScreen`
  * - `./pages/Dashboard`
- * - `./pages/KanbanBoard`
  * - `./pages/Sessions`
  * - `./pages/SessionDetail`
  * - `./pages/ActivityFeed`
- * - `./pages/Analytics`
  * - `./pages/Workflows`
  * - `./pages/Settings`
  * - `./pages/CcConfig`
@@ -66,11 +64,9 @@ import { Layout } from "./components/Layout";
 import { DocumentTitle } from "./components/DocumentTitle";
 import { SplashScreen } from "./components/SplashScreen";
 import { Dashboard } from "./pages/Dashboard";
-import { KanbanBoard } from "./pages/KanbanBoard";
 import { Sessions } from "./pages/Sessions";
 import { SessionDetail } from "./pages/SessionDetail";
 import { ActivityFeed } from "./pages/ActivityFeed";
-import { Analytics } from "./pages/Analytics";
 import { Workflows } from "./pages/Workflows";
 import { Settings } from "./pages/Settings";
 import { CcConfig } from "./pages/CcConfig";
@@ -101,11 +97,9 @@ export default function App() {
         <Routes>
           <Route element={<Layout wsConnected={connected} />}>
             <Route index element={<Dashboard />} />
-            <Route path="kanban" element={<KanbanBoard />} />
             <Route path="sessions" element={<Sessions />} />
             <Route path="sessions/:id" element={<SessionDetail />} />
             <Route path="activity" element={<ActivityFeed />} />
-            <Route path="analytics" element={<Analytics />} />
             <Route path="workflows" element={<Workflows />} />
             <Route path="lanes" element={<Navigate to="/run" replace />} />
             <Route path="cc-config" element={<CcConfig />} />