CSS: add StaticColorStripSource type with auto-sized LED count

Introduces a new 'static' source type that fills all device LEDs with a
single constant RGB color — no screen capture or processing required.

- StaticColorStripSource storage model (color + led_count=0 auto-size)
- StaticColorStripStream: no background thread, configure() sizes to device
  LED count at processor start; hot-updates preserve runtime size
- ColorStripStreamManager dispatches static sources (no LiveStream needed)
- WledTargetProcessor calls stream.configure(device_led_count) on start
- API schemas/routes: source_type Literal["picture","static"]; color field;
  overlay/calibration-test endpoints return 400 for static
- Frontend: type selector modal, color picker, type-aware card rendering
  (🎨 icon + color swatch), LED count field hidden for static type
- Locale keys: color_strip.type, color_strip.static_color (en + ru)

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

server/src/wled_controller/static/js/app.js

@@ -90,6 +90,7 @@ import {
 // Layer 5: color-strip sources
 import {
     showCSSEditor, closeCSSEditorModal, forceCSSEditorClose, saveCSSEditor, deleteColorStrip,
+    onCSSTypeChange,
 } from './features/color-strips.js';
 
 // Layer 5: calibration
@@ -274,6 +275,7 @@ Object.assign(window, {
     forceCSSEditorClose,
     saveCSSEditor,
     deleteColorStrip,
+    onCSSTypeChange,
 
     // calibration
     showCalibration,