Add IconSelect for filter types, audio modes, engine descriptions; fix scroll flash

- Filter type picker: IconSelect with 3-column grid, auto-add on select, removed redundant + button
- Audio mode picker: IconSelect with SVG visualizations for RMS/Peak/Beat
- Capture engine grid: added per-engine icons and localized descriptions
- Fixed scroll flash during icon grid open animation (settled class after transitionend)

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

server/src/wled_controller/static/locales/en.json

@@ -63,6 +63,12 @@
   "templates.engine.select": "Select an engine...",
   "templates.engine.unavailable": "Unavailable",
   "templates.engine.unavailable.hint": "This engine is not available on your system",
+  "templates.engine.mss.desc": "Cross-platform, pure Python",
+  "templates.engine.dxcam.desc": "DirectX, low latency",
+  "templates.engine.bettercam.desc": "DirectX, high performance",
+  "templates.engine.camera.desc": "USB/IP camera capture",
+  "templates.engine.scrcpy.desc": "Android screen mirror",
+  "templates.engine.wgc.desc": "Windows Graphics Capture",
   "templates.config": "Configuration",
   "templates.config.show": "Show configuration",
   "templates.config.none": "No additional configuration",
@@ -1063,6 +1069,9 @@
   "value_source.mode.rms": "RMS (Volume)",
   "value_source.mode.peak": "Peak",
   "value_source.mode.beat": "Beat",
+  "value_source.mode.rms.desc": "Average volume level",
+  "value_source.mode.peak.desc": "Loudest moment tracking",
+  "value_source.mode.beat.desc": "Rhythm pulse detection",
   "value_source.auto_gain": "Auto Gain:",
   "value_source.auto_gain.hint": "Automatically normalize audio levels so output uses the full range, regardless of input volume",
   "value_source.auto_gain.enable": "Enable auto-gain",