Add visual IconSelect selectors for effect, palette, gradient, waveform dropdowns

Replace plain <select> dropdowns with rich visual selectors:
- Effect type: icon grid with descriptions
- Effect/audio palette: gradient strip previews from color data
- Gradient preset: gradient strip previews (13 presets)
- Audio visualization: icon grid with descriptions
- Notification effect: icon grid with descriptions
- Waveform (value source): inline SVG shape previews

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

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

@@ -840,8 +840,11 @@
   "color_strip.notification.effect": "Effect:",
   "color_strip.notification.effect.hint": "Visual effect when a notification fires. Flash fades linearly, Pulse uses a smooth bell curve, Sweep fills LEDs left-to-right then fades.",
   "color_strip.notification.effect.flash": "Flash",
+  "color_strip.notification.effect.flash.desc": "Instant on, linear fade-out",
   "color_strip.notification.effect.pulse": "Pulse",
+  "color_strip.notification.effect.pulse.desc": "Smooth bell-curve glow",
   "color_strip.notification.effect.sweep": "Sweep",
+  "color_strip.notification.effect.sweep.desc": "Fills left-to-right then fades",
   "color_strip.notification.duration": "Duration (ms):",
   "color_strip.notification.duration.hint": "How long the notification effect plays, in milliseconds.",
   "color_strip.notification.default_color": "Default Color:",
@@ -888,8 +891,11 @@
   "color_strip.audio.visualization": "Visualization:",
   "color_strip.audio.visualization.hint": "How audio data is rendered to LEDs.",
   "color_strip.audio.viz.spectrum": "Spectrum Analyzer",
+  "color_strip.audio.viz.spectrum.desc": "Frequency bars across the strip",
   "color_strip.audio.viz.beat_pulse": "Beat Pulse",
+  "color_strip.audio.viz.beat_pulse.desc": "All LEDs pulse on the beat",
   "color_strip.audio.viz.vu_meter": "VU Meter",
+  "color_strip.audio.viz.vu_meter.desc": "Volume level fills the strip",
   "color_strip.audio.source": "Audio Source:",
   "color_strip.audio.source.hint": "Audio source for this visualization. Can be a multichannel (device) or mono (single channel) source. Create and manage audio sources in the Sources tab.",
   "color_strip.audio.sensitivity": "Sensitivity:",