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/zh.json

@@ -348,8 +348,7 @@
   "filters.select_type": "选择滤镜类型...",
   "filters.add": "添加滤镜",
   "filters.remove": "移除",
-  "filters.move_up": "上移",
-  "filters.move_down": "下移",
+  "filters.drag_to_reorder": "拖动以重新排序",
   "filters.empty": "尚未添加滤镜。使用下方选择器添加滤镜。",
   "filters.brightness": "亮度",
   "filters.saturation": "饱和度",
@@ -360,6 +359,9 @@
   "filters.flip": "翻转",
   "filters.color_correction": "色彩校正",
   "filters.filter_template": "滤镜模板",
+  "filters.frame_interpolation": "帧插值",
+  "filters.noise_gate": "噪声门",
+  "filters.palette_quantization": "调色板量化",
   "postprocessing.description_label": "描述（可选）：",
   "postprocessing.description_placeholder": "描述此模板...",
   "postprocessing.created": "模板创建成功",