Fix settings persistence, streaming stability, and UI polish

- Fix device settings partial update using model_fields_set for true merge
- Add missing interpolation_mode and smoothing to all API responses
- Fix send_pixels race condition when wled_client is None during stop
- Allow LED segments to exceed edge pixel count (float stepping)
- Fix modal scroll lock using position:fixed to prevent layout shift
- Show loading state for brightness slider until real value is fetched
- Remove stream description from stream selector dialog

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/core/processor_manager.py

@@ -613,6 +613,8 @@ class ProcessorManager:
                         )
 
                     # Send to WLED with device brightness
+                    if not state.is_running or state.wled_client is None:
+                        break
                     brightness_value = int(wled_brightness * 255)
                     await state.wled_client.send_pixels(led_colors, brightness=brightness_value)
 

server/src/wled_controller/core/screen_capture.py

@@ -229,18 +229,16 @@ def get_edge_segments(
         divide_axis = 0  # Height
         edge_length = edge_pixels.shape[0]
 
-    if segment_count > edge_length:
-        raise ValueError(
-            f"segment_count {segment_count} is larger than edge length {edge_length}"
-        )
-
-    # Calculate segment size
-    segment_size = edge_length // segment_count
+    # Use float stepping so multiple LEDs can share pixels when
+    # segment_count > edge_length (e.g. after downscaling).
+    step = edge_length / segment_count
 
     segments = []
     for i in range(segment_count):
-        start = i * segment_size
-        end = start + segment_size if i < segment_count - 1 else edge_length
+        start = int(i * step)
+        end = max(start + 1, int((i + 1) * step))
+        # Clamp to edge bounds
+        end = min(end, edge_length)
 
         if divide_axis == 1:
             segment = edge_pixels[:, start:end, :]