fix: reuse upload credentials for device config sync

- load server sync creds from db/upload_creds.env like uploads do
- fall back from YARIS_DEVICE_KEY to existing YARIS_API_KEY
- document shared credential flow for server-synced identity
- add test coverage for sync credential fallback

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

modules/app_device_sync.py

@@ -10,6 +10,7 @@ import threading
 import time
 
 import requests
+from dotenv import load_dotenv
 
 from . import app_network, app_sql
 
@@ -18,6 +19,9 @@ _SYNC_THREAD = None
 _SYNC_STOP = False
 _SYNC_CONFIG_VERSION = 0  # Track last-synced version to detect changes
 _RELOAD_CALLBACK = None
+_BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+
+load_dotenv(os.path.join(_BASE_DIR, "db", "upload_creds.env"))
 
 
 def _has_internet():
@@ -34,6 +38,12 @@ def _has_internet():
         return False
 
 
+def _server_credentials():
+    server_url = os.getenv("YARIS_SERVER_URL", "").rstrip("/")
+    device_key = os.getenv("YARIS_DEVICE_KEY") or os.getenv("YARIS_API_KEY", "")
+    return server_url, device_key
+
+
 def start_sync():
     """Start background device config sync thread."""
     global _SYNC_THREAD, _SYNC_STOP
@@ -61,8 +71,7 @@ def _sync_loop():
     """Periodically sync device config from server when internet available."""
     global _SYNC_CONFIG_VERSION
     
-    server_url = os.getenv("YARIS_SERVER_URL", "")
-    device_key = os.getenv("YARIS_DEVICE_KEY", "")
+    server_url, device_key = _server_credentials()
     
     if not server_url or not device_key:
         return  # Sync disabled if server URL or device key not configured
@@ -125,7 +134,8 @@ def _on_config_changed():
 
 def is_sync_enabled():
     """Check if device config sync from server is enabled."""
-    return bool(os.getenv("YARIS_SERVER_URL")) and bool(os.getenv("YARIS_DEVICE_KEY"))
+    server_url, device_key = _server_credentials()
+    return bool(server_url) and bool(device_key)
 
 
 def get_synced_config_version():