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.

README.md

@@ -21,7 +21,7 @@ Internal build — all rights reserved.
   rendered with xterm.js) attached to a lane's directory — the exact TUI you'd
   see locally, fully interactive, resumable, and attachable from a real
   terminal too via `ccam lanes shell`.
-- **Analytics, alerts, Kanban and a workflow view**, plus an MCP server and a CLI.
+- **Analytics (in-dashboard tab), alerts, and a workflow view**, plus an MCP server and a CLI.
 
 ## Requirements