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/sync_clocks.py

@@ -20,6 +20,7 @@ from wled_controller.storage.sync_clock_store import SyncClockStore
 from wled_controller.storage.color_strip_store import ColorStripStore
 from wled_controller.core.processing.sync_clock_manager import SyncClockManager
 from wled_controller.utils import get_logger
+from wled_controller.storage.base_store import EntityNotFoundError
 
 logger = get_logger(__name__)
 
@@ -34,7 +35,7 @@ def _to_response(clock: SyncClock, manager: SyncClockManager) -> SyncClockRespon
         name=clock.name,
         speed=rt.speed if rt else clock.speed,
         description=clock.description,
-        tags=getattr(clock, 'tags', []),
+        tags=clock.tags,
         is_running=rt.is_running if rt else True,
         elapsed_time=rt.get_time() if rt else 0.0,
         created_at=clock.created_at,
@@ -73,6 +74,9 @@ async def create_sync_clock(
         )
         fire_entity_event("sync_clock", "created", clock.id)
         return _to_response(clock, manager)
+    except EntityNotFoundError as e:
+        raise HTTPException(status_code=404, detail=str(e))
+
     except ValueError as e:
         raise HTTPException(status_code=400, detail=str(e))
 
@@ -114,6 +118,9 @@ async def update_sync_clock(
             manager.update_speed(clock_id, clock.speed)
         fire_entity_event("sync_clock", "updated", clock_id)
         return _to_response(clock, manager)
+    except EntityNotFoundError as e:
+        raise HTTPException(status_code=404, detail=str(e))
+
     except ValueError as e:
         raise HTTPException(status_code=400, detail=str(e))
 
@@ -137,6 +144,9 @@ async def delete_sync_clock(
         manager.release_all_for(clock_id)
         store.delete_clock(clock_id)
         fire_entity_event("sync_clock", "deleted", clock_id)
+    except EntityNotFoundError as e:
+        raise HTTPException(status_code=404, detail=str(e))
+
     except ValueError as e:
         raise HTTPException(status_code=400, detail=str(e))