Introduce Picture Targets to separate processing from devices

Add PictureTarget entity that bridges PictureSource to output device,
separating processing settings from device connection/calibration state.
This enables future target types (Art-Net, E1.31) and cleanly decouples
"what to stream" from "where to stream."

- Add PictureTarget/WledPictureTarget dataclasses and storage
- Split ProcessorManager into DeviceState (health) + TargetState (processing)
- Add /api/v1/picture-targets endpoints (CRUD, start/stop, settings, metrics)
- Simplify device API (remove processing/settings/metrics endpoints)
- Auto-migrate existing device settings to picture targets on first startup
- Add Targets tab to WebUI with target cards and editor modal
- Add en/ru locale keys for targets UI

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

server/src/wled_controller/api/routes/picture_sources.py

@@ -14,6 +14,7 @@ from wled_controller.api.auth import AuthRequired
 from wled_controller.api.dependencies import (
     get_device_store,
     get_picture_source_store,
+    get_picture_target_store,
     get_pp_template_store,
     get_processor_manager,
     get_template_store,
@@ -36,6 +37,7 @@ from wled_controller.core.capture_engines import EngineRegistry
 from wled_controller.core.filters import FilterRegistry, ImagePool
 from wled_controller.core.processor_manager import ProcessorManager
 from wled_controller.storage import DeviceStore
+from wled_controller.storage.picture_target_store import PictureTargetStore
 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
@@ -256,16 +258,16 @@ async def delete_picture_source(
     stream_id: str,
     _auth: AuthRequired,
     store: PictureSourceStore = Depends(get_picture_source_store),
-    device_store: DeviceStore = Depends(get_device_store),
+    target_store: PictureTargetStore = Depends(get_picture_target_store),
 ):
     """Delete a picture source."""
     try:
-        # Check if any device references this stream
-        if store.is_referenced_by_device(stream_id, device_store):
+        # Check if any target references this stream
+        if store.is_referenced_by_target(stream_id, target_store):
             raise HTTPException(
                 status_code=409,
-                detail="Cannot delete picture source: it is assigned to one or more devices. "
-                       "Please reassign those devices before deleting.",
+                detail="Cannot delete picture source: it is assigned to one or more targets. "
+                       "Please reassign those targets before deleting.",
             )
         store.delete_stream(stream_id)
     except HTTPException: