feat: rewrite busylight as FastAPI web application with SQLite

Replace the standalone Python script + config.cfg with a full web
application featuring:
- FastAPI backend with REST API
- SQLite database (config, state, activity log separated)
- Bootstrap 5 web interface for configuration
- Pages: Dashboard, Users, Devices, Assignments, Color Rules, Settings, Log
- APScheduler background polling for Teams presence + AIDA status
- systemd service file for Linux deployment
- Migration script to import existing config.cfg data

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

busylight.service

@@ -0,0 +1,17 @@
+[Unit]
+Description=Busylight WLED Controller
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+User=busylight
+Group=busylight
+WorkingDirectory=/opt/busylight
+ExecStart=/opt/busylight/venv/bin/python app.py
+Restart=always
+RestartSec=10
+Environment=PYTHONUNBUFFERED=1
+
+[Install]
+WantedBy=multi-user.target