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/static/locales/en.json

@@ -348,8 +348,7 @@
   "filters.select_type": "Select filter type...",
   "filters.add": "Add Filter",
   "filters.remove": "Remove",
-  "filters.move_up": "Move Up",
-  "filters.move_down": "Move Down",
+  "filters.drag_to_reorder": "Drag to reorder",
   "filters.empty": "No filters added. Use the selector below to add filters.",
   "filters.brightness": "Brightness",
   "filters.saturation": "Saturation",
@@ -360,6 +359,9 @@
   "filters.flip": "Flip",
   "filters.color_correction": "Color Correction",
   "filters.filter_template": "Filter Template",
+  "filters.frame_interpolation": "Frame Interpolation",
+  "filters.noise_gate": "Noise Gate",
+  "filters.palette_quantization": "Palette Quantization",
   "postprocessing.description_label": "Description (optional):",
   "postprocessing.description_placeholder": "Describe this template...",
   "postprocessing.created": "Template created successfully",