Rewrite HAOS integration: target-centric architecture with KC color sensors

- Rewrite integration to target-centric model: each picture target becomes
  a HA device under a server hub with switch, FPS, and status sensors
- Replace KC light entities with color sensors (hex state + RGB attributes)
  for better automation support via WebSocket real-time updates
- Add WebSocket manager for Key Colors color streaming
- Add KC per-stage timing metrics (calc_colors, broadcast) with rolling avg
- Fix KC timing fields missing from API by adding them to Pydantic schema
- Make start/stop processing idempotent to prevent intermittent 404 errors
- Add HAOS localization support (en, ru) using translation_key system
- Rename integration from "WLED Screen Controller" to "LED Screen Controller"
- Remove obsolete select.py (display select) and README.md

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

custom_components/wled_screen_controller/strings.json

@@ -2,20 +2,49 @@
   "config": {
     "step": {
       "user": {
-        "title": "Set up WLED Screen Controller",
-        "description": "Enter the URL of your WLED Screen Controller server",
+        "title": "Set up LED Screen Controller",
+        "description": "Enter the URL and API key for your LED Screen Controller server.",
         "data": {
-          "name": "Name",
-          "server_url": "Server URL"
+          "server_url": "Server URL",
+          "api_key": "API Key"
+        },
+        "data_description": {
+          "server_url": "URL of your LED Screen Controller server (e.g., http://192.168.1.100:8080)",
+          "api_key": "API key from your server's configuration file"
         }
       }
     },
     "error": {
-      "cannot_connect": "Failed to connect to server. Check the URL and ensure the server is running.",
-      "unknown": "Unexpected error occurred"
+      "cannot_connect": "Failed to connect to server.",
+      "invalid_api_key": "Invalid API key.",
+      "unknown": "Unexpected error occurred."
     },
     "abort": {
-      "already_configured": "This server is already configured"
+      "already_configured": "This server is already configured."
+    }
+  },
+  "entity": {
+    "switch": {
+      "processing": {
+        "name": "Processing"
+      }
+    },
+    "sensor": {
+      "fps": {
+        "name": "FPS"
+      },
+      "status": {
+        "name": "Status",
+        "state": {
+          "processing": "Processing",
+          "idle": "Idle",
+          "error": "Error",
+          "unavailable": "Unavailable"
+        }
+      },
+      "rectangle_color": {
+        "name": "{rectangle_name} Color"
+      }
     }
   }
 }