feat(monitor): add real-time monitoring dashboard with Redis persistence
Complete observability solution for production deployments with terminal-style UI.
**Backend Implementation:**
- `monitor.py`: Stats manager tracking requests, browsers, errors, timeline data
- `monitor_routes.py`: REST API endpoints for all monitor functionality
- GET /monitor/health - System health snapshot
- GET /monitor/requests - Active & completed requests
- GET /monitor/browsers - Browser pool details
- GET /monitor/endpoints/stats - Aggregated endpoint analytics
- GET /monitor/timeline - Time-series data (memory, requests, browsers)
- GET /monitor/logs/{janitor,errors} - Event logs
- POST /monitor/actions/{cleanup,kill_browser,restart_browser} - Control actions
- POST /monitor/stats/reset - Reset counters
- Redis persistence for endpoint stats (survives restart)
- Timeline tracking (5min window, 5s resolution, 60 data points)
**Frontend Dashboard** (`/dashboard`):
- **System Health Bar**: CPU%, Memory%, Network I/O, Uptime
- **Pool Status**: Live counts (permanent/hot/cold browsers + memory)
- **Live Activity Tabs**:
- Requests: Active (realtime) + recent completed (last 100)
- Browsers: Detailed table with actions (kill/restart)
- Janitor: Cleanup event log with timestamps
- Errors: Recent errors with stack traces
- **Endpoint Analytics**: Count, avg latency, success%, pool hit%
- **Resource Timeline**: SVG charts (memory/requests/browsers) with terminal aesthetics
- **Control Actions**: Force cleanup, restart permanent, reset stats
- **Auto-refresh**: 5s polling (toggleable)
**Integration:**
- Janitor events tracked (close_cold, close_hot, promote)
- Crawler pool promotion events logged
- Timeline updater background task (5s interval)
- Lifespan hooks for monitor initialization
**UI Design:**
- Terminal vibe matching Crawl4AI theme
- Dark background, cyan/pink accents, monospace font
- Neon glow effects on charts
- Responsive layout, hover interactions
- Cross-navigation: Playground ↔ Monitor
**Key Features:**
- Zero-config: Works out of the box with existing Redis
- Real-time visibility into pool efficiency
- Manual browser management (kill/restart)
- Historical data persistence
- DevOps-friendly UX
Routes:
- API: `/monitor/*` (backend endpoints)
- UI: `/dashboard` (static HTML)
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