Add target FPS slider to Capture Settings and remove unused HACS workflow

- Add Target FPS slider (range 10-90) to Capture Settings dialog
- Fix settings PUT to merge with current values instead of resetting defaults
- Update FPS validation range to 10-90 in schema and config
- Remove irrelevant .github/workflows/validate.yml (HACS leftover)

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

server/src/wled_controller/api/schemas.py

@@ -79,7 +79,7 @@ class ProcessingSettings(BaseModel):
     """Processing settings for a device."""
 
     display_index: int = Field(default=0, description="Display to capture", ge=0)
-    fps: int = Field(default=30, description="Target frames per second", ge=1, le=60)
+    fps: int = Field(default=30, description="Target frames per second", ge=10, le=90)
     border_width: int = Field(default=10, description="Border width in pixels", ge=1, le=100)
     brightness: float = Field(default=1.0, description="Global brightness (0.0-1.0)", ge=0.0, le=1.0)
     state_check_interval: int = Field(