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/locales/en.json

@@ -630,13 +630,13 @@
   "scenes.description.hint": "Optional description of what this scene does",
   "scenes.color": "Card Color:",
   "scenes.color.hint": "Accent color for the scene card on the dashboard",
+  "scenes.targets": "Targets:",
+  "scenes.targets.hint": "Select which targets to include in this scene snapshot",
   "scenes.capture": "Capture",
   "scenes.activate": "Activate scene",
   "scenes.recapture": "Recapture current state",
   "scenes.delete": "Delete scene",
   "scenes.targets_count": "targets",
-  "scenes.devices_count": "devices",
-  "scenes.automations_count": "automations",
   "scenes.captured": "Scene captured",
   "scenes.updated": "Scene updated",
   "scenes.activated": "Scene activated",