Add value sources for dynamic brightness control on LED targets

Introduces a new Value Source entity that produces a scalar float (0.0-1.0)
for dynamic brightness modulation. Three subtypes: Static (constant),
Animated (sine/triangle/square/sawtooth waveform), and Audio-reactive
(RMS/peak/beat from mono audio source). Value sources can be optionally
attached to LED targets to control brightness each frame.

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

server/src/wled_controller/templates/index.html

@@ -118,6 +118,7 @@
     {% include 'modals/pp-template.html' %}
     {% include 'modals/profile-editor.html' %}
     {% include 'modals/audio-source-editor.html' %}
+    {% include 'modals/value-source-editor.html' %}
 
     {% include 'partials/tutorial-overlay.html' %}
     {% include 'partials/image-lightbox.html' %}