Phase 25.5a: Server-side device config API and Pi sync thread

- Created app_device_sync.py: background sync thread with connectivity-driven scheduling (5min online, 60sec backoff when offline)
- Server /api/device-config endpoints: GET for Pi device auth, POST for admin user auth
- Database migration adds config_version, owner_name, car_model, device_name, avatar_path to devices table
- Pi syncs config from server on network availability; offline-first design (loads from local JSON at startup)
- Settings UI fields read-only when server sync enabled

All 63 tests passing. Ready for testing with actual server connection.

Co-authored-by: Copilot <[email protected]>

app.py

@@ -1,5 +1,5 @@
 from flask import Flask, render_template, make_response, json, jsonify, request, send_file, Response
-from modules import app_gps, app_events, app_car, app_account, app_obd, app_sql, app_dash, app_upload, app_video, app_health, app_alerts, app_settings, app_network, app_device_config
+from modules import app_gps, app_events, app_car, app_account, app_obd, app_sql, app_dash, app_upload, app_video, app_health, app_alerts, app_settings, app_network, app_device_config, app_device_sync
 import os, time
 from gevent.pywsgi import WSGIServer
 
@@ -14,6 +14,7 @@ gps = app_gps.start_gps()
 app_sql.start_logging()
 app_upload.start_uploading()
 app_alerts.start_alerting()
+app_device_sync.start_sync()
 
 @app.route('/')
 def index():