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>

app.py

@@ -38,9 +38,13 @@ async def lifespan(application: FastAPI):
     # Start background polling
     interval = int(database.get_setting("poll_interval", "15"))
     bg_scheduler.add_job(scheduler.poll_status, "interval", seconds=interval, id="poll")
+    bg_scheduler.add_job(scheduler.check_devices, "interval", seconds=240, id="device_check")
     bg_scheduler.start()
     logger.info("Polling gestartet (Intervall: %ds)", interval)
 
+    # Initial device check
+    scheduler.check_devices()
+
     yield
 
     bg_scheduler.shutdown()
@@ -195,8 +199,13 @@ async def devices_page(request: Request):
     devices = conn.execute(
         "SELECT * FROM wled_devices ORDER BY name, hostname"
     ).fetchall()
+    last_check_row = conn.execute(
+        "SELECT MAX(last_check) as lc FROM wled_devices WHERE last_check IS NOT NULL"
+    ).fetchone()
     conn.close()
-    return templates.TemplateResponse(*_ctx(request, "devices", devices=devices))
+    last_check = last_check_row["lc"] if last_check_row and last_check_row["lc"] else None
+    return templates.TemplateResponse(*_ctx(request, "devices",
+        devices=devices, last_check=last_check))
 
 
 @app.post("/api/devices")
@@ -241,15 +250,10 @@ async def delete_device(device_id: int):
     return RedirectResponse("/devices", status_code=303)
 
 
-@app.get("/api/devices/{device_id}/status")
-async def device_status(device_id: int):
-    from wled_client import get_wled_info
-    conn = database.get_db()
-    dev = conn.execute("SELECT hostname FROM wled_devices WHERE id=?", (device_id,)).fetchone()
-    conn.close()
-    if not dev:
-        return {"online": False}
-    return get_wled_info(dev["hostname"])
+@app.post("/api/devices/check-all")
+async def check_all_devices():
+    scheduler.check_devices()
+    return RedirectResponse("/devices", status_code=303)
 
 
 # ── Assignments ────────────────────────────────────────────────────────────