Add navi_ui form component with client-side validation ...

- Add Form UI component schema in navi/mcp/ui_server/components/form.py
- Support text, textarea, number, email, url, select, multiselect, checkbox, date fields
- Implement hidden user message mode for form submissions (is_display=False, is_context=True)
- Add WebSocket form_submit handling and _start_agent_run helper
- Render forms client-side with real-time JS validation in webclient
- Submit once guard via localStorage and replace form with read-only summary
- Provide wsSend via Vue provide/inject in ChatArea
- Add tests for backend form component, websocket form_submit, and frontend Form.vue
- Update docs/tools.md and docs/websocket.md
- Build production webclient dist

Co-Authored-By: Claude <noreply@anthropic.com>

Step 3: Extract AntiStallMonitor from run_stream() ...

- Create navi/core/anti_stall.py with AntiStallMonitor class
- Encapsulates stall detection (todo progress + repeated tool calls)
- Encapsulates adaptive re-plan (failed todo step detection)
- Provides init() / pre_turn() / post_turn() two-phase interface
- Remove ~50 lines of stall/replan logic from agent.py run_stream()
- Remove _todo_status_snapshot and _todo_failed_steps helpers from agent.py
- Update AgentTurnContext: remove stall fields (now live in AntiStallMonitor)
- Add 13 unit tests for pre_turn and post_turn behavior

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>