Fix browser freeze on print completion with camera stream open

Root cause: When a print completed with the camera stream popup open,
spawning a second ffmpeg process for finish photo capture caused a
conflict that froze the browser tab and video window.

Solution: Buffer the last frame from active camera streams. When
capturing finish photo, use the buffered frame if a stream is active
instead of spawning a new ffmpeg process.

Backend changes:
- camera.py: Added _last_frames buffer and get_buffered_frame() helper
- main.py: Photo capture uses buffered frame when stream is active
- main.py: Moved slow operations to background tasks (energy calc,
  photo capture, smart plug, notifications, maintenance)
- archive.py: Fixed sync file write blocking event loop (asyncio.to_thread)
- printers.py: Added debug endpoint to simulate print completion

Frontend changes:
- useWebSocket.ts: Throttled printer status updates (100ms) to prevent
  UI overload from rapid WebSocket messages
- useWebSocket.ts: Debounced archive invalidations (3s) to prevent
  cascade of re-renders on print completion
- useWebSocket.test.ts: Updated tests for throttled/debounced handlers

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

deploy/bambuddy.service

@@ -0,0 +1,31 @@
+[Unit]
+Description=BamBuddy Print Archive
+After=network.target
+
+[Service]
+Type=simple
+User=claude
+Group=claude
+WorkingDirectory=/opt/claude/projects/bambuddy
+Environment="PATH=/opt/claude/projects/bambuddy/venv/bin"
+
+# Force kill after 10 seconds if graceful shutdown fails
+TimeoutStopSec=10
+
+# Kill any zombie ffmpeg processes before starting/after stopping
+ExecStartPre=-/usr/bin/pkill -9 ffmpeg
+ExecStopPost=-/usr/bin/pkill -9 ffmpeg
+
+# Ensure directories exist and have correct permissions before starting
+# The + prefix runs the command as root even though User=claude
+ExecStartPre=+/bin/mkdir -p /opt/claude/projects/bambuddy/logs
+ExecStartPre=+/bin/mkdir -p /opt/claude/projects/bambuddy/archive
+ExecStartPre=+/bin/chown -R claude:claude /opt/claude/projects/bambuddy/logs
+ExecStartPre=+/bin/chown -R claude:claude /opt/claude/projects/bambuddy/archive
+
+ExecStart=/opt/claude/projects/bambuddy/venv/bin/uvicorn backend.app.main:app --host 0.0.0.0 --port 8000
+Restart=always
+RestartSec=10
+
+[Install]
+WantedBy=multi-user.target