feat: background device status check every 240s instead of on page load

- Add online, leds, version, last_check columns to wled_devices table
- Background job checks all WLED devices every 4 minutes
- Initial check on startup
- Devices page reads status from DB (instant page load)
- 'Alle jetzt pruefen' button triggers manual check

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

scheduler.py

@@ -3,7 +3,7 @@ import os
 from datetime import datetime
 
 from database import get_db, get_setting, log_activity
-from wled_client import build_wled_url, call_wled
+from wled_client import build_wled_url, call_wled, get_wled_info
 
 logger = logging.getLogger(__name__)
 
@@ -197,3 +197,29 @@ def _process_user(user, aida_lines, settings, conn):
         display_name, aida_status or "-", teams_status,
         "aktualisiert" if wled_changed else "nur Dashboard",
     )
+
+
+def check_devices():
+    """Check all WLED devices and store status in DB. Called periodically."""
+    conn = get_db()
+    try:
+        devices = conn.execute("SELECT id, hostname FROM wled_devices").fetchall()
+        for dev in devices:
+            info = get_wled_info(dev["hostname"])
+            conn.execute("""
+                UPDATE wled_devices
+                SET online=?, leds=?, version=?, last_check=?
+                WHERE id=?
+            """, (
+                1 if info.get("online") else 0,
+                info.get("leds", 0) if info.get("online") else 0,
+                info.get("version", "") if info.get("online") else "",
+                datetime.now(),
+                dev["id"],
+            ))
+        conn.commit()
+        logger.info("Device-Check: %d Geraete geprueft", len(devices))
+    except Exception as e:
+        logger.error("Device-Check Fehler: %s", e)
+    finally:
+        conn.close()