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/css/streams.css

@@ -345,6 +345,17 @@
     width: 100%;
 }
 
+.pp-filter-text-input {
+    width: 100%;
+    padding: 4px 8px;
+    border: 1px solid var(--border-color);
+    border-radius: 4px;
+    background: var(--card-bg);
+    color: var(--text-primary);
+    font-size: 12px;
+    font-family: monospace;
+}
+
 .pp-filter-option-bool label {
     justify-content: space-between;
     gap: 8px;
@@ -392,6 +403,61 @@
     order: 0;
 }
 
+/* ── PP filter drag-and-drop ── */
+
+.pp-filter-drag-handle {
+    cursor: grab;
+    opacity: 0;
+    color: var(--text-secondary);
+    font-size: 12px;
+    line-height: 1;
+    padding: 2px 4px;
+    border-radius: 3px;
+    transition: opacity 0.2s ease;
+    user-select: none;
+    touch-action: none;
+    flex-shrink: 0;
+}
+
+.pp-filter-card:hover .pp-filter-drag-handle {
+    opacity: 0.5;
+}
+
+.pp-filter-drag-handle:hover {
+    opacity: 1 !important;
+    background: var(--border-color);
+}
+
+.pp-filter-drag-handle:active {
+    cursor: grabbing;
+}
+
+.pp-filter-drag-clone {
+    position: fixed;
+    z-index: 9999;
+    pointer-events: none;
+    opacity: 0.92;
+    transform: scale(1.02);
+    box-shadow: 0 12px 36px rgba(0, 0, 0, 0.25);
+    will-change: top;
+}
+
+.pp-filter-drag-placeholder {
+    border: 2px dashed var(--primary-color);
+    border-radius: 8px;
+    background: rgba(33, 150, 243, 0.04);
+    min-height: 42px;
+    transition: height 0.15s ease;
+}
+
+body.pp-filter-dragging .pp-filter-card {
+    transition: none !important;
+}
+
+body.pp-filter-dragging .pp-filter-drag-handle {
+    opacity: 0 !important;
+}
+
 .pp-add-filter-row {
     display: flex;
     gap: 8px;