feat: add WLED device status check (online/offline, LEDs, version)

- Query WLED JSON API (/json/info) for device info
- Show online/offline status dot, LED count and firmware version
- Auto-check all devices on page load
- Button to manually check individual or all devices
- Fix hostname placeholder to volksheimstaette.de

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

app.py

@@ -243,6 +243,17 @@ 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"])
+
+
 # ── Assignments ────────────────────────────────────────────────────────────
 
 @app.get("/assignments", response_class=HTMLResponse)