feat: 初始化 PicAnalysis 项目

完整的前后端图片分析应用，包含：
- 后端：Express + Prisma + SQLite，101个单元测试全部通过
- 前端：React + TypeScript + Vite，47个单元测试，89.73%覆盖率
- E2E测试：Playwright 测试套件
- MCP集成：Playwright MCP配置完成并测试通过

功能模块：
- 用户认证（JWT）
- 文档管理（CRUD）
- 待办管理（三态工作流）
- 图片管理（上传、截图、OCR）

测试覆盖：
- 后端单元测试：101/101 ✅
- 前端单元测试：47/47 ✅
- E2E测试：通过 ✅
- MCP Playwright测试：通过 ✅

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

backend/src/services/ocr.service.ts

@@ -0,0 +1,115 @@
+/**
+ * OCR Service
+ * Handles OCR processing and confidence validation
+ */
+
+export interface OCRResult {
+  text: string;
+  confidence: number;
+  shouldCreateDocument: boolean;
+}
+
+export interface OCRProviderOptions {
+  timeout?: number;
+  retries?: number;
+}
+
+export class OCRService {
+  private static readonly DEFAULT_TIMEOUT = 10000; // 10 seconds
+  private static readonly DEFAULT_RETRIES = 2;
+
+  /**
+   * Determine if document should be created based on confidence
+   * @param confidence - OCR confidence score (0-1)
+   * @param threshold - Minimum threshold (default 0.3)
+   * @returns boolean - True if document should be created
+   */
+  static shouldCreateDocument(
+    confidence: number,
+    threshold: number = 0.3
+  ): boolean {
+    // Validate inputs
+    if (!this.isValidConfidence(confidence)) {
+      return false;
+    }
+
+    return confidence >= threshold;
+  }
+
+  /**
+   * Validate confidence score is in valid range
+   * @param confidence - Confidence score to validate
+   * @returns boolean - True if valid
+   */
+  static isValidConfidence(confidence: number): boolean {
+    return typeof confidence === 'number' &&
+           !isNaN(confidence) &&
+           confidence >= 0 &&
+           confidence <= 1;
+  }
+
+  /**
+   * Get initial processing status
+   * @returns string - Initial status
+   */
+  static getInitialStatus(): string {
+    return 'pending';
+  }
+
+  /**
+   * Process OCR with retry logic
+   * @param imageId - Image ID to process
+   * @param provider - OCR provider function
+   * @param options - OCR options
+   * @returns Promise<OCRResult> - OCR result
+   */
+  static async process(
+    imageId: string,
+    provider: (id: string) => Promise<{ text: string; confidence: number }>,
+    options: OCRProviderOptions = {}
+  ): Promise<OCRResult> {
+    const timeout = options.timeout ?? this.DEFAULT_TIMEOUT;
+    const retries = options.retries ?? this.DEFAULT_RETRIES;
+
+    let lastError: Error | null = null;
+
+    for (let attempt = 0; attempt <= retries; attempt++) {
+      try {
+        // Add timeout to provider call
+        const result = await Promise.race([
+          provider(imageId),
+          new Promise<never>((_, reject) =>
+            setTimeout(() => reject(new Error('OCR timeout')), timeout)
+          ),
+        ]);
+
+        const shouldCreate = this.shouldCreateDocument(result.confidence);
+
+        return {
+          text: result.text,
+          confidence: result.confidence,
+          shouldCreateDocument: shouldCreate,
+        };
+      } catch (error) {
+        lastError = error as Error;
+
+        // Don't retry on certain errors
+        if (
+          error instanceof Error &&
+          (error.message === 'invalid image format' ||
+           error.message.includes('Invalid'))
+        ) {
+          throw error;
+        }
+
+        // Retry on transient errors
+        if (attempt < retries) {
+          await new Promise((resolve) => setTimeout(resolve, 1000 * (attempt + 1)));
+          continue;
+        }
+      }
+    }
+
+    throw lastError || new Error('OCR processing failed');
+  }
+}