Add CSPT entity, processed CSS source type, reverse filter, and UI improvements

- Add Color Strip Processing Template (CSPT) entity: reusable filter chains
  for 1D LED strip postprocessing (backend, storage, API, frontend CRUD)
- Add "processed" color strip source type that wraps another CSS source and
  applies a CSPT filter chain (dataclass, stream, schema, modal, cards)
- Add Reverse filter for strip LED order reversal
- Add CSPT and processed CSS nodes/edges to visual graph editor
- Add CSPT test preview WS endpoint with input source selection
- Add device settings CSPT template selector (add + edit modals with hints)
- Use icon grids for palette quantization preset selector in filter lists
- Use EntitySelect for template references and test modal source selectors
- Fix filters.css_filter_template.desc missing localization
- Fix icon grid cell height inequality (grid-auto-rows: 1fr)
- Rename "Processed" subtab to "Processing Templates"
- Localize all new strings (en/ru/zh)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/wled_controller/templates/modals/test-css-source.html

@@ -44,6 +44,12 @@
                 <canvas id="css-test-layers-axis" class="css-test-strip-axis"></canvas>
             </div>
 
+            <!-- CSPT test: input source selector (hidden by default) -->
+            <div id="css-test-cspt-input-group" style="display:none" class="css-test-led-control">
+                <label for="css-test-cspt-input-select" data-i18n="color_strip.processed.input">Input Source:</label>
+                <select id="css-test-cspt-input-select" class="css-test-cspt-select" onchange="applyCssTestSettings()"></select>
+            </div>
+
             <!-- LED count & FPS controls -->
             <div class="css-test-led-control">
                 <span id="css-test-led-group">