Add audio sources as first-class entities, add mapped CSS type, simplify target editor for mapped sources

- Audio sources moved to separate tab with dedicated CRUD API, store, and editor modal
- New "mapped" color strip source type: assigns different CSS sources to distinct LED sub-ranges (zones)
- Mapped stream runtime with per-zone sub-streams, auto-sizing, hot-update support
- Target editor auto-collapses segments UI when mapped CSS is selected
- Delete protection for CSS sources referenced by mapped zones
- Compact header/footer layout

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

server/src/wled_controller/config.py

@@ -34,6 +34,7 @@ class StorageConfig(BaseSettings):
     picture_targets_file: str = "data/picture_targets.json"
     pattern_templates_file: str = "data/pattern_templates.json"
     color_strip_sources_file: str = "data/color_strip_sources.json"
+    audio_sources_file: str = "data/audio_sources.json"
     profiles_file: str = "data/profiles.json"