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/css/components.css

@@ -413,3 +413,27 @@ textarea:focus-visible {
     border-color: var(--primary-color);
     box-shadow: 0 0 0 2px rgba(76, 175, 80, 0.2);
 }
+
+/* Scene target selector */
+.scene-target-add-row {
+    display: flex;
+    gap: 6px;
+    margin-bottom: 8px;
+}
+.scene-target-add-row select { flex: 1; }
+.scene-target-add-row .btn { padding: 4px 10px; min-width: 0; flex: 0 0 auto; font-size: 0.85rem; }
+.scene-target-list {
+    display: flex;
+    flex-direction: column;
+    gap: 4px;
+}
+.scene-target-item {
+    display: flex;
+    align-items: center;
+    justify-content: space-between;
+    padding: 6px 10px;
+    border: 1px solid var(--border-color);
+    border-radius: var(--radius);
+    background: var(--bg-primary);
+    font-size: 0.9rem;
+}