fix: UI polish — notification history buttons, CSS test error handling, schedule time picker, empty state labels

- Notification history: replace text buttons with icon buttons, use modal-footer for proper positioning
- CSS test: reject 0-LED picture sources with clear error message, show WS close reason in UI
- Calibration: distribute LEDs by aspect ratio (16:9 default) instead of evenly across edges
- Value source schedule: replace native time input with custom HH:MM picker matching automation style
- Remove "No ... yet" empty state labels from all CardSection instances

server/src/wled_controller/api/routes/color_strip_sources.py

@@ -829,6 +829,15 @@ async def test_color_strip_ws(
     if hasattr(stream, "configure"):
         stream.configure(max(1, led_count))
 
+    # Reject picture sources with 0 calibration LEDs (no edges configured)
+    if stream.led_count <= 0:
+        csm.release(source_id, consumer_id)
+        await websocket.close(
+            code=4005,
+            reason="No LEDs configured. Open Calibration and set LED counts for each edge.",
+        )
+        return
+
     # Clamp FPS to sane range
     fps = max(1, min(60, fps))
     _frame_interval = 1.0 / fps