refactor: 删除历史遗留的 selectedHumanId/selectedElementId 字段

这两个字段是早期数字人方案的遗留，当前业务已完全不使用：
- types/project.ts: 删除字段定义
- store/projectStore.ts: 删除 setSelectedHumanId/setSelectedAvatarInfo action
- api/modules/localStorage.ts: 删除序列化
- VideoCreation/index.tsx: 删除加载恢复逻辑
- utils/projectMeta.ts: 删除默认值

当前素材选择实际只有：
- 人物素材: avatarMaterialPath/Name/Duration（对口型用）
- 空镜素材: userUploadedMaterials + emptyShotMaterial

tauri-app/src/api/modules/localStorage.ts

@@ -99,8 +99,6 @@ export const localProjectApi = {
       coverPath: meta.coverPath,
       finalVideoPath: meta.finalVideoPath,
       exportedAt: meta.exportedAt,
-      selectedHumanId: meta.selectedHumanId,
-      selectedElementId: meta.selectedElementId,
       selectedVoiceId: meta.selectedVoiceId,
       composedVideoUrl: meta.composedVideoUrl,
       composedVideoPath: meta.composedVideoPath,

tauri-app/src/pages/VideoCreation/index.tsx

@@ -64,8 +64,6 @@ function VideoCreationContent() {
           if (meta.subtitleAlignment !== undefined) updates.subtitleAlignment = meta.subtitleAlignment;
 
           // Step 3 视频生成
-          if (meta.selectedElementId !== undefined) updates.selectedElementId = meta.selectedElementId;
-          if (meta.selectedHumanId !== undefined) updates.selectedHumanId = meta.selectedHumanId;
           if (meta.avatarMaterialPath !== undefined) updates.avatarMaterialPath = meta.avatarMaterialPath;
           if (meta.avatarMaterialName !== undefined) updates.avatarMaterialName = meta.avatarMaterialName;
           if (meta.avatarMaterialDuration !== undefined) updates.avatarMaterialDuration = meta.avatarMaterialDuration;

tauri-app/src/store/projectStore.ts

@@ -21,8 +21,6 @@ interface ProjectActions {
   setTopic: (topic: string) => void;
   setTitle: (title: string) => void;
   setCurrentStep: (step: number) => void;
-  setSelectedHumanId: (id: string | undefined) => void;
-  setSelectedAvatarInfo: (humanId?: string, elementId?: number, voiceId?: string) => void;
   setAvatarMaterial: (path?: string, name?: string, duration?: number) => void;
   setSelectedVoiceId: (voiceId: string) => void;
   setFinalVideoPath: (path: string | undefined) => void;
@@ -173,21 +171,6 @@ export const useProjectStore = create<ProjectStore>()(
             state.currentStep = step;
           }),
 
-        setSelectedHumanId: id => {
-          set(state => {
-            state.selectedHumanId = id;
-            state.updatedAt = Date.now();
-          });
-          // 不再即时落盘，统一在视频生成完成回调中保存到 meta.json
-        },
-        setSelectedAvatarInfo: (humanId, elementId, voiceId) => {
-          set(state => {
-            state.selectedHumanId = humanId;
-            state.selectedElementId = elementId;
-            state.selectedVoiceId = voiceId;
-            state.updatedAt = Date.now();
-          });
-        },
         setAvatarMaterial: (path, name, duration) => {
           set(state => {
             state.avatarMaterialPath = path;
@@ -254,7 +237,7 @@ export const useProjectStore = create<ProjectStore>()(
         partialize: (state) => ({
           // 只保存 UI 状态，不保存项目业务数据
           _isLoading: state._isLoading,
-          // 不保存: segments, selectedHumanId, finalVideoPath, coverPath 等
+          // 不保存: segments, finalVideoPath, coverPath 等
         }),
         onRehydrateStorage: () => state => {
           if (state) {

tauri-app/src/types/project.ts

@@ -83,8 +83,6 @@ export interface ProjectMeta {
   topic?: string;
 
   // === 素材选择 ===
-  selectedHumanId?: string;
-  selectedElementId?: number;
   selectedVoiceId?: string;
   avatarMaterialPath?: string;
   avatarMaterialName?: string;

tauri-app/src/utils/projectMeta.ts

@@ -148,8 +148,6 @@ export function migrateMeta(raw: Record<string, any>): Partial<ProjectMeta> {
  */
 export const BLANK_META_OVERRIDES: MetaOverrides = {
   topic: undefined,
-  selectedHumanId: undefined,
-  selectedElementId: undefined,
   selectedVoiceId: undefined,
   finalVideoPath: undefined,
   coverPath: undefined,