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/components/DocumentTitle.tsx

@@ -24,12 +24,8 @@ export function DocumentTitle() {
     title = `${t("sessions")} · ${sessionId.slice(0, 8)}`;
   } else if (path.startsWith("/sessions")) {
     title = t("sessions");
-  } else if (path.startsWith("/kanban")) {
-    title = t("agentBoard");
   } else if (path.startsWith("/activity")) {
     title = t("activityFeed");
-  } else if (path.startsWith("/analytics")) {
-    title = t("analytics");
   } else if (path.startsWith("/workflows")) {
     title = t("workflows");
   } else if (path.startsWith("/cc-config")) {