Add Key Colors target type for extracting colors from screen regions

Introduce a new "key_colors" target type alongside WLED targets, enabling
real-time color extraction from configurable screen rectangles with
average/median/dominant modes, temporal smoothing, and WebSocket streaming.

- Split WledPictureTarget into its own module, add KeyColorsPictureTarget
- Add KC target lifecycle to ProcessorManager (register, start/stop, processing loop)
- Extend API routes and schemas for KC targets (CRUD, settings, state, metrics, colors)
- Add WebSocket endpoint for real-time color updates with auth
- Add KC sub-tab in Targets UI with editor modal and live color swatches
- Add EN and RU translations for all key colors strings

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

server/src/wled_controller/main.py

@@ -19,7 +19,8 @@ from wled_controller.storage.template_store import TemplateStore
 from wled_controller.storage.postprocessing_template_store import PostprocessingTemplateStore
 from wled_controller.storage.picture_source_store import PictureSourceStore
 from wled_controller.storage.picture_target_store import PictureTargetStore
-from wled_controller.storage.picture_target import WledPictureTarget
+from wled_controller.storage.wled_picture_target import WledPictureTarget
+from wled_controller.storage.key_colors_picture_target import KeyColorsPictureTarget
 from wled_controller.utils import setup_logging, get_logger
 
 # Initialize logging
@@ -172,6 +173,17 @@ async def lifespan(app: FastAPI):
                 logger.info(f"Registered target: {target.name} ({target.id})")
             except Exception as e:
                 logger.error(f"Failed to register target {target.id}: {e}")
+        elif isinstance(target, KeyColorsPictureTarget):
+            try:
+                processor_manager.add_kc_target(
+                    target_id=target.id,
+                    picture_source_id=target.picture_source_id,
+                    settings=target.settings,
+                )
+                registered_targets += 1
+                logger.info(f"Registered KC target: {target.name} ({target.id})")
+            except Exception as e:
+                logger.error(f"Failed to register KC target {target.id}: {e}")
 
     logger.info(f"Registered {registered_targets} picture target(s)")