Add motion detection to camera server

🔍 New features:
- motion.py: Frame differencing motion detector
- Background thread compares frames continuously
- Configurable threshold, cooldown, sensitivity
- POSTs events + snapshot to collector

📡 New endpoints:
- GET /motion/stats - Detection statistics
- POST /motion/enable - Start detection
- POST /motion/disable - Stop detection

⚙️ Configuration (in .env):
- MOTION_ENABLED: true/false
- MOTION_THRESHOLD: Pixel diff threshold
- MOTION_COOLDOWN: Seconds between events
- COLLECTOR_URL: Where to POST events

Next: Event collector in vixy-mcp 🦊

server/README.md

@@ -0,0 +1,66 @@
+# vixy-vision Server
+
+Camera snapshot server with motion detection for Raspberry Pi.
+
+## Quick Start
+
+```bash
+./setup.sh
+sudo systemctl start vixy-vision
+```
+
+## Features
+
+- 📷 USB camera snapshots via HTTPS API
+- 🔐 API key authentication  
+- 🔍 Motion detection with frame differencing
+- 📤 Event reporting to central collector
+- 🔄 Auto-reconnect on camera failure
+
+## Configuration
+
+Copy `env.example` to `.env` and customize:
+
+```bash
+cp env.example .env
+nano .env
+```
+
+Key settings:
+
+| Variable | Description | Default |
+|----------|-------------|---------|
+| `API_KEY` | Auth key for API | (required) |
+| `CAMERA_ID` | Identifier for this camera | camera |
+| `MOTION_ENABLED` | Enable motion detection | false |
+| `MOTION_THRESHOLD` | Sensitivity (lower = more) | 25 |
+| `MOTION_COOLDOWN` | Seconds between events | 5.0 |
+| `COLLECTOR_URL` | Where to POST events | (optional) |
+
+## API Endpoints
+
+| Endpoint | Auth | Description |
+|----------|------|-------------|
+| `GET /` | No | Service info |
+| `GET /health` | No | Health check |
+| `GET /snapshot` | Yes | JPEG snapshot |
+| `GET /motion/stats` | Yes | Detection stats |
+| `POST /motion/enable` | Yes | Start detection |
+| `POST /motion/disable` | Yes | Stop detection |
+
+## Motion Events
+
+When motion is detected, the server POSTs to `COLLECTOR_URL`:
+
+```json
+{
+  "event": {
+    "timestamp": "2024-12-16T14:23:01Z",
+    "camera_id": "basement",
+    "event_type": "motion",
+    "confidence": 0.75,
+    "area_percent": 7.5
+  },
+  "snapshot": "<base64 JPEG>"
+}
+```