Add noise gate, palette quantization filters and drag-and-drop filter ordering

- Add noise gate filter: suppresses per-pixel color flicker below threshold
  using stateful frame comparison with pre-allocated int16 buffers
- Add palette quantization filter: maps pixels to nearest color in preset
  or custom hex palette, using chunked processing for memory efficiency
- Add "string" option type to filter schema system (base, API, frontend)
- Replace up/down buttons with pointer-event drag-and-drop in PP template
  filter list, with clone/placeholder feedback and modal auto-scroll
- Add frame_interpolation locale keys (was missing from all 3 locales)
- Update TODO.md: mark completed processing pipeline items

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

server/src/wled_controller/api/schemas/filters.py

@@ -17,12 +17,13 @@ class FilterOptionDefSchema(BaseModel):
 
     key: str = Field(description="Option key")
     label: str = Field(description="Display label")
-    type: str = Field(description="Option type (float, int, bool, or select)")
+    type: str = Field(description="Option type (float, int, bool, select, or string)")
     default: Any = Field(description="Default value")
     min_value: Any = Field(description="Minimum value")
     max_value: Any = Field(description="Maximum value")
     step: Any = Field(description="Step increment")
     choices: Optional[List[Dict[str, str]]] = Field(default=None, description="Available choices for select type")
+    max_length: Optional[int] = Field(default=None, description="Maximum string length for string type")
 
 
 class FilterTypeResponse(BaseModel):