feat: unify reference image data structure, add Nano Banana 2 model

Reference Image 统一重构:
- 新增 ReferenceImage 类型 (src/types/index.ts)，统一承载 base64 和 localPath 两种来源
- 重写 image-ref-store.ts：单一 Map<string, ReferenceImage[]> 替代原来的
  imageGenRefStore + lastGeneratedImagePaths 双通路
  - sessionStorage 持久化 last-generated 路径，解决页面刷新后数据丢失
  - buildReferenceImages() 作为唯一的 merge 入口，消除各组件手写拼接逻辑
- ImageGenConfirmation props 从两个 (referenceImagePaths + referenceImagesData)
  合并为单一 referenceImages?: ReferenceImage[]
  - 预览渲染改为单循环，根据 data/localPath 决定 img src，上传图和结果图同时显示
  - API 调用时再拆分回 base64 和路径两个字段，后端无需改动
- StreamingMessage / MessageItem 各自 5 行手动 merge 逻辑替换为一行
  buildReferenceImages() 调用
- ChatView 改用 setLastGeneratedImages() 和 transferPendingToMessage()
  替代直接操作 Map
- MessageInput 改用 setRefImages() / deleteRefImages() 替代直接操作 Map

新增 Gemini 3.1 Flash Image 模型:
- 新增 Nano Banana 2 (gemini-3.1-flash-image-preview) 作为默认图片生成模型
- 模型列表: Nano Banana 2 > Nano Banana Pro > Nano Banana
- 更新 ProviderManager、image-generator.ts、media/generate route 的默认值

其他已有改动一并提交:
- batch image generation 功能文件
- 依赖更新 (package.json / package-lock.json)
- i18n、db schema、AppShell、uploads route 等相关改动

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

src/types/index.ts

@@ -406,6 +406,16 @@ export const SETTING_KEYS = {
   MAX_THINKING_TOKENS: 'max_thinking_tokens',
 } as const;
 
+// ==========================================
+// Reference Image Types (for image generation)
+// ==========================================
+
+export interface ReferenceImage {
+  mimeType: string;
+  data?: string;       // base64 (user upload)
+  localPath?: string;  // file path (generated result)
+}
+
 // ==========================================
 // File Attachment Types
 // ==========================================
@@ -435,6 +445,145 @@ export function formatFileSize(bytes: number): string {
 // Claude Client Types
 // ==========================================
 
+// ==========================================
+// Batch Image Generation Types
+// ==========================================
+
+export type MediaJobStatus = 'draft' | 'planning' | 'planned' | 'running' | 'paused' | 'completed' | 'cancelled' | 'failed';
+export type MediaJobItemStatus = 'pending' | 'processing' | 'completed' | 'failed' | 'cancelled';
+
+export interface MediaJob {
+  id: string;
+  session_id: string | null;
+  status: MediaJobStatus;
+  doc_paths: string;       // JSON array of file paths
+  style_prompt: string;
+  batch_config: string;    // JSON of BatchConfig
+  total_items: number;
+  completed_items: number;
+  failed_items: number;
+  created_at: string;
+  updated_at: string;
+  completed_at: string | null;
+}
+
+export interface MediaJobItem {
+  id: string;
+  job_id: string;
+  idx: number;
+  prompt: string;
+  aspect_ratio: string;
+  image_size: string;
+  model: string;
+  tags: string;            // JSON array of strings
+  source_refs: string;     // JSON array of strings
+  status: MediaJobItemStatus;
+  retry_count: number;
+  result_media_generation_id: string | null;
+  error: string | null;
+  created_at: string;
+  updated_at: string;
+}
+
+export interface MediaContextEvent {
+  id: string;
+  session_id: string;
+  job_id: string;
+  payload: string;         // JSON object
+  sync_mode: 'manual' | 'auto_batch';
+  synced_at: string | null;
+  created_at: string;
+}
+
+export interface BatchConfig {
+  concurrency: number;     // max parallel image generations (default: 2)
+  maxRetries: number;      // max retry attempts per item (default: 2)
+  retryDelayMs: number;    // base delay for exponential backoff (default: 2000)
+}
+
+export interface PlannerItem {
+  prompt: string;
+  aspectRatio: string;
+  resolution: string;
+  tags: string[];
+  sourceRefs: string[];
+}
+
+export interface PlannerOutput {
+  summary: string;
+  items: PlannerItem[];
+}
+
+export type JobProgressEventType =
+  | 'item_started'
+  | 'item_completed'
+  | 'item_failed'
+  | 'item_retry'
+  | 'job_completed'
+  | 'job_paused'
+  | 'job_cancelled';
+
+export interface JobProgressEvent {
+  type: JobProgressEventType;
+  jobId: string;
+  itemId?: string;
+  itemIdx?: number;
+  progress: {
+    total: number;
+    completed: number;
+    failed: number;
+    processing: number;
+  };
+  error?: string;
+  retryCount?: number;
+  mediaGenerationId?: string;
+  timestamp: string;
+}
+
+// --- Batch Image Gen API Types ---
+
+export interface CreateMediaJobRequest {
+  sessionId?: string;
+  items: Array<{
+    prompt: string;
+    aspectRatio?: string;
+    imageSize?: string;
+    model?: string;
+    tags?: string[];
+    sourceRefs?: string[];
+  }>;
+  batchConfig?: Partial<BatchConfig>;
+  stylePrompt?: string;
+  docPaths?: string[];
+}
+
+export interface PlanMediaJobRequest {
+  docPaths?: string[];
+  docContent?: string;
+  stylePrompt: string;
+  sessionId?: string;
+  count?: number;
+}
+
+export interface UpdateMediaJobItemsRequest {
+  items: Array<{
+    id: string;
+    prompt?: string;
+    aspectRatio?: string;
+    imageSize?: string;
+    tags?: string[];
+  }>;
+}
+
+export interface MediaJobResponse {
+  job: MediaJob;
+  items: MediaJobItem[];
+}
+
+export interface MediaJobListResponse {
+  jobs: MediaJob[];
+}
+
 export interface ClaudeStreamOptions {
   prompt: string;
   sessionId: string;