Expose device brightness as HA number entity

Add a Number platform to the HAOS integration so each LED target
with a brightness-capable device gets a 0-255 slider in Home
Assistant. Coordinator now fetches device list and brightness on
each poll cycle. Also enable chart animation in perf-charts.

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

custom_components/wled_screen_controller/strings.json

@@ -45,6 +45,11 @@
       "rectangle_color": {
         "name": "{rectangle_name} Color"
       }
+    },
+    "number": {
+      "brightness": {
+        "name": "Brightness"
+      }
     }
   }
 }