ui: redesign Tuerschilder page as card grid with all device info

- Card per device showing: hostname, MAC, version, LEDs, segments
- Segment assignments displayed per card
- Last activity timestamp
- Online/offline dot in card header
- Action buttons in card footer
- Add device + firmware upload side by side at bottom

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

app.py

@@ -335,6 +335,14 @@ async def devices_page(request: Request):
         """, (dev["hostname"],)).fetchone()
         d = dict(dev)
         d["last_activity"] = last_act["la"] if last_act and last_act["la"] else None
+        # Segment assignments for this device
+        d["segments"] = conn.execute("""
+            SELECT a.segment, u.display_name
+            FROM assignments a
+            JOIN users u ON u.azure_id = a.user_azure_id
+            WHERE a.wled_device_id = ?
+            ORDER BY a.segment
+        """, (dev["id"],)).fetchall()
         devices.append(d)
     last_check_row = conn.execute(
         "SELECT MAX(last_check) as lc FROM wled_devices WHERE last_check IS NOT NULL"