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/env.example

@@ -0,0 +1,47 @@
+# vixy-vision Server Configuration
+# Copy to .env and customize
+
+# ============ Required ============
+
+# API Key for authentication (generate with: python3 -c 'import secrets; print(secrets.token_urlsafe(32))')
+API_KEY=your-secret-key-here
+
+# Camera identifier (used in events)
+CAMERA_ID=basement
+
+# ============ Camera Settings ============
+
+# Camera device index (0 = first USB camera)
+CAMERA_INDEX=0
+
+# Resolution (camera will use closest supported)
+CAMERA_WIDTH=1920
+CAMERA_HEIGHT=1080
+
+# JPEG quality (1-100)
+JPEG_QUALITY=85
+
+# ============ Motion Detection ============
+
+# Enable motion detection (true/false)
+MOTION_ENABLED=true
+
+# Pixel difference threshold (lower = more sensitive)
+MOTION_THRESHOLD=25
+
+# Minimum % of frame that must change to trigger event
+MOTION_MIN_AREA=0.5
+
+# Seconds between motion events (prevents spam)
+MOTION_COOLDOWN=5.0
+
+# Seconds between frame checks
+MOTION_INTERVAL=0.5
+
+# ============ Event Collector ============
+
+# URL to POST motion events to (on Mac mini)
+COLLECTOR_URL=http://192.168.1.50:8780/events
+
+# API key for collector (optional)
+COLLECTOR_API_KEY=