Simplify scenes to capture only target state, add target selector

- Remove DeviceBrightnessSnapshot and AutomationSnapshot from scene data model
- Simplify capture_current_snapshot and apply_scene_state to targets only
- Remove device/automation dependencies from scene preset API routes
- Add target selector (combobox + add/remove) to scene capture modal
- Fix stale profiles reference bug in scene_preset_store recapture
- Update automation engine call sites for simplified scene functions
- Sync scene presets cache between automations and scene-presets modules

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

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

@@ -85,6 +85,7 @@ import {
 import {
     openScenePresetCapture, editScenePreset, saveScenePreset, closeScenePresetEditor,
     activateScenePreset, recaptureScenePreset, deleteScenePreset,
+    addSceneTarget, removeSceneTarget,
 } from './features/scene-presets.js';
 
 // Layer 5: device-discovery, targets
@@ -318,6 +319,8 @@ Object.assign(window, {
     activateScenePreset,
     recaptureScenePreset,
     deleteScenePreset,
+    addSceneTarget,
+    removeSceneTarget,
 
     // device-discovery
     onDeviceTypeChanged,