feat: add built-in Kanban board to web UI

[chetan-guevara]

Summary

Adds a built-in Kanban board as a native tab in the ClaudeClaw web UI — no external server, no iframe, no configuration required. Task state is persisted to .claude/claudeclaw/kanban.json alongside existing ClaudeClaw data.

Features

• Three columns: To Do → In Progress → Done
• Add tasks via a modal (+ Add task button)
• Clear done column with one click
• Auto-refresh every 10 seconds
• Agent auto-tracking (when used with the agent lifecycle PR feat: surface sub-agent lifecycle events in chat #41): sub-agent spawns automatically add a card to In Progress; completions move it to Done
• Fully consistent with the existing ClaudeClaw UI aesthetic

Architecture

New service: src/ui/services/kanban.ts

Handles all reads/writes to .claude/claudeclaw/kanban.json:

• readKanban() — reads the board, initialises missing columns gracefully
• writeKanban(board) — persists to disk
• addCardToColumn(column, card) — atomic add
• moveCard(id, toColumn, patch?) — atomic move across columns

New API endpoints in server.ts

• GET /api/kanban — returns the full board JSON
• POST /api/kanban — writes the full board JSON

Board data schema

{
  "columns": {
    "todo": [],
    "in_progress": [],
    "done": []
  }
}

Each card:

{
  id: string;
  title: string;
  description?: string;
  started_at?: string;
  completed_at?: string;
  agent_type?: string;
}

Note on agent auto-tracking

The kanban service is self-contained and works standalone. When combined with PR #41 (agent lifecycle tracking), the server.ts chat endpoint can call addCardToColumn / moveCard to automatically track sub-agent activity — but this PR does not depend on #41 and can be merged independently.

Test plan

• Open http://127.0.0.1:4632, click the Kanban tab
• Click + Add task, fill in title and description → card appears in To Do
• Reload page → board state is restored from kanban.json
• Click Clear on Done column → done cards removed
• Verify .claude/claudeclaw/kanban.json is written correctly after each action
• Verify Dashboard tab still works normally