Backend performance and code quality improvements

Performance (hot path):
- Fix double brightness: removed duplicate scaling from 9 device clients
  (wled, adalight, ambiled, openrgb, hue, spi, chroma, gamesense, usbhid,
  espnow) — processor loop is now the single source of brightness
- Bounded send_timestamps deque with maxlen, removed 3 cleanup loops
- Running FPS sum O(1) instead of sum()/len() O(n) per frame
- datetime.now(timezone.utc) → time.monotonic() with lazy conversion
- Device info refresh interval 30 → 300 iterations
- Composite: gate layer_snapshots copy on preview client flag
- Composite: versioned sub_streams snapshot (copy only on change)
- Composite: pre-resolved blend methods (dict lookup vs getattr)
- ApiInput: np.copyto in-place instead of astype allocation

Code quality:
- BaseJsonStore: RLock on get/delete/get_all/count (was created but unused)
- EntityNotFoundError → proper 404 responses across 15 route files
- Remove 21 defensive getattr(x,'tags',[]) — field guaranteed on all models
- Fix Dict[str,any] → Dict[str,Any] in template/audio_template stores
- Log 4 silenced exceptions (automation engine, metrics, system)
- ValueStream.get_value() now @abstractmethod
- Config.from_yaml: add encoding="utf-8"
- OutputTargetStore: remove 25-line _load override, use _legacy_json_keys
- BaseJsonStore: add _legacy_json_keys for migration support
- Remove unnecessary except Exception→500 from postprocessing list endpoint

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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

@@ -19,6 +19,7 @@ from wled_controller.core.audio.factory import AudioEngineRegistry
 from wled_controller.storage.audio_template_store import AudioTemplateStore
 from wled_controller.storage.audio_source_store import AudioSourceStore
 from wled_controller.utils import get_logger
+from wled_controller.storage.base_store import EntityNotFoundError
 
 logger = get_logger(__name__)
 
@@ -38,7 +39,7 @@ async def list_audio_templates(
         responses = [
             AudioTemplateResponse(
                 id=t.id, name=t.name, engine_type=t.engine_type,
-                engine_config=t.engine_config, tags=getattr(t, 'tags', []),
+                engine_config=t.engine_config, tags=t.tags,
                 created_at=t.created_at,
                 updated_at=t.updated_at, description=t.description,
             )
@@ -66,10 +67,13 @@ async def create_audio_template(
         fire_entity_event("audio_template", "created", template.id)
         return AudioTemplateResponse(
             id=template.id, name=template.name, engine_type=template.engine_type,
-            engine_config=template.engine_config, tags=getattr(template, 'tags', []),
+            engine_config=template.engine_config, tags=template.tags,
             created_at=template.created_at,
             updated_at=template.updated_at, description=template.description,
         )
+    except EntityNotFoundError as e:
+        raise HTTPException(status_code=404, detail=str(e))
+
     except ValueError as e:
         raise HTTPException(status_code=400, detail=str(e))
     except Exception as e:
@@ -90,7 +94,7 @@ async def get_audio_template(
         raise HTTPException(status_code=404, detail=f"Audio template {template_id} not found")
     return AudioTemplateResponse(
         id=t.id, name=t.name, engine_type=t.engine_type,
-        engine_config=t.engine_config, tags=getattr(t, 'tags', []),
+        engine_config=t.engine_config, tags=t.tags,
         created_at=t.created_at,
         updated_at=t.updated_at, description=t.description,
     )
@@ -113,10 +117,13 @@ async def update_audio_template(
         fire_entity_event("audio_template", "updated", template_id)
         return AudioTemplateResponse(
             id=t.id, name=t.name, engine_type=t.engine_type,
-            engine_config=t.engine_config, tags=getattr(t, 'tags', []),
+            engine_config=t.engine_config, tags=t.tags,
             created_at=t.created_at,
             updated_at=t.updated_at, description=t.description,
         )
+    except EntityNotFoundError as e:
+        raise HTTPException(status_code=404, detail=str(e))
+
     except ValueError as e:
         raise HTTPException(status_code=400, detail=str(e))
     except Exception as e:
@@ -137,6 +144,9 @@ async def delete_audio_template(
         fire_entity_event("audio_template", "deleted", template_id)
     except HTTPException:
         raise
+    except EntityNotFoundError as e:
+        raise HTTPException(status_code=404, detail=str(e))
+
     except ValueError as e:
         raise HTTPException(status_code=400, detail=str(e))
     except Exception as e: