Introduce ColorStripSource as first-class entity

Extracts color processing and calibration out of WledPictureTarget into a
new PictureColorStripSource entity, enabling multiple LED targets to share
one capture/processing pipeline.

New entities & processing:
- storage/color_strip_source.py: ColorStripSource + PictureColorStripSource models
- storage/color_strip_store.py: JSON-backed CRUD store (prefix css_)
- core/processing/color_strip_stream.py: ColorStripStream ABC + PictureColorStripStream (runs border-extract → map → smooth → brightness/sat/gamma in background thread)
- core/processing/color_strip_stream_manager.py: ref-counted shared stream manager

Modified storage/processing:
- WledPictureTarget simplified to device_id + color_strip_source_id + standby_interval + state_check_interval
- Device model: calibration field removed
- WledTargetProcessor: acquires ColorStripStream from manager instead of running its own pipeline
- ProcessorManager: wires ColorStripStreamManager into TargetContext

API layer:
- New routes: GET/POST/PUT/DELETE /api/v1/color-strip-sources, PUT calibration/test
- Removed calibration endpoints from /devices
- Updated /picture-targets CRUD for new target structure

Frontend:
- New color-strips.js module with CSS editor modal and card rendering
- Calibration modal extended with CSS mode (css-id hidden field + device picker)
- targets.js: Color Strip Sources section added to LED tab; target editor/card updated
- app.js: imports and window globals for CSS + showCSSCalibration
- en.json / ru.json: color_strip.* and targets.section.color_strips keys added

Data migration runs at startup: existing WledPictureTargets are converted to
reference a new PictureColorStripSource created from their old settings.

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

server/src/wled_controller/api/dependencies.py

@@ -7,6 +7,7 @@ from wled_controller.storage.postprocessing_template_store import Postprocessing
 from wled_controller.storage.pattern_template_store import PatternTemplateStore
 from wled_controller.storage.picture_source_store import PictureSourceStore
 from wled_controller.storage.picture_target_store import PictureTargetStore
+from wled_controller.storage.color_strip_store import ColorStripStore
 from wled_controller.storage.profile_store import ProfileStore
 from wled_controller.core.profiles.profile_engine import ProfileEngine
 
@@ -17,6 +18,7 @@ _pp_template_store: PostprocessingTemplateStore | None = None
 _pattern_template_store: PatternTemplateStore | None = None
 _picture_source_store: PictureSourceStore | None = None
 _picture_target_store: PictureTargetStore | None = None
+_color_strip_store: ColorStripStore | None = None
 _processor_manager: ProcessorManager | None = None
 _profile_store: ProfileStore | None = None
 _profile_engine: ProfileEngine | None = None
@@ -64,6 +66,13 @@ def get_picture_target_store() -> PictureTargetStore:
     return _picture_target_store
 
 
+def get_color_strip_store() -> ColorStripStore:
+    """Get color strip store dependency."""
+    if _color_strip_store is None:
+        raise RuntimeError("Color strip store not initialized")
+    return _color_strip_store
+
+
 def get_processor_manager() -> ProcessorManager:
     """Get processor manager dependency."""
     if _processor_manager is None:
@@ -93,13 +102,14 @@ def init_dependencies(
     pattern_template_store: PatternTemplateStore | None = None,
     picture_source_store: PictureSourceStore | None = None,
     picture_target_store: PictureTargetStore | None = None,
+    color_strip_store: ColorStripStore | None = None,
     profile_store: ProfileStore | None = None,
     profile_engine: ProfileEngine | None = None,
 ):
     """Initialize global dependencies."""
     global _device_store, _template_store, _processor_manager
     global _pp_template_store, _pattern_template_store, _picture_source_store, _picture_target_store
-    global _profile_store, _profile_engine
+    global _color_strip_store, _profile_store, _profile_engine
     _device_store = device_store
     _template_store = template_store
     _processor_manager = processor_manager
@@ -107,5 +117,6 @@ def init_dependencies(
     _pattern_template_store = pattern_template_store
     _picture_source_store = picture_source_store
     _picture_target_store = picture_target_store
+    _color_strip_store = color_strip_store
     _profile_store = profile_store
     _profile_engine = profile_engine