Replace HAOS light entity with select entities, add zero-brightness optimization

- Remove light.py platform (static color control via HA light entity)
- Add select.py with CSS Source and Brightness Source dropdowns for LED targets
- Coordinator now fetches color-strip-sources and value-sources lists
- Add generic update_target() method for partial target updates
- Clean up stale device registry entries on integration reload
- Skip frame sends when effective brightness is ~0 (suppresses unnecessary
  UDP/HTTP traffic while LEDs are dark)

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

custom_components/wled_screen_controller/strings.json

@@ -53,9 +53,12 @@
         "name": "Brightness"
       }
     },
-    "light": {
-      "light": {
-        "name": "Light"
+    "select": {
+      "color_strip_source": {
+        "name": "Color Strip Source"
+      },
+      "brightness_source": {
+        "name": "Brightness Source"
       }
     }
   }