feat(server): add OCR invoice processing functionality

New endpoints:
- server/src/app/api/v1/endpoints/ocr.py: OCR API endpoints for invoice scanning

New schemas:
- server/src/app/schemas/ocr.py: OCR request/response data schemas

New services:
- server/src/app/services/ocr.py: OCR processing business logic
- server/src/app/services/expense_claims.py: expense claims management service

Scripts:
- server/scripts/bootstrap_paddleocr_mobile.sh: PaddleOCR mobile setup script
- server/scripts/paddle_ocr_worker.py: PaddleOCR worker process

server/src/app/schemas/ocr.py

@@ -0,0 +1,35 @@
+from __future__ import annotations
+
+from pydantic import BaseModel, Field
+
+
+class OcrRecognizeLineRead(BaseModel):
+    text: str = Field(description="识别出的文本行。")
+    score: float = Field(default=0.0, ge=0.0, le=1.0, description="该行识别置信度。")
+    box: list[list[int]] = Field(default_factory=list, description="文本框坐标。")
+    page_index: int | None = Field(default=None, description="页码，从 0 开始。")
+
+
+class OcrRecognizeDocumentRead(BaseModel):
+    filename: str = Field(description="原始文件名。")
+    media_type: str = Field(description="文件媒体类型。")
+    engine: str = Field(default="paddleocr_mobile", description="使用的 OCR 引擎。")
+    model: str = Field(default="PP-OCRv5_mobile", description="模型族标识。")
+    text: str = Field(default="", description="合并后的完整 OCR 文本。")
+    summary: str = Field(default="", description="供对话和语义层复用的简短摘要。")
+    avg_score: float = Field(default=0.0, ge=0.0, le=1.0, description="平均识别置信度。")
+    line_count: int = Field(default=0, ge=0, description="文本行数。")
+    page_count: int = Field(default=1, ge=0, description="识别页数。")
+    warnings: list[str] = Field(default_factory=list, description="该文件的识别提示或警告。")
+    lines: list[OcrRecognizeLineRead] = Field(default_factory=list, description="逐行识别结果。")
+
+
+class OcrRecognizeBatchRead(BaseModel):
+    engine: str = Field(default="paddleocr_mobile", description="使用的 OCR 引擎。")
+    model: str = Field(default="PP-OCRv5_mobile", description="模型族标识。")
+    total_file_count: int = Field(default=0, ge=0, description="本次上传的总文件数。")
+    success_count: int = Field(default=0, ge=0, description="成功进入 OCR 的文件数。")
+    documents: list[OcrRecognizeDocumentRead] = Field(
+        default_factory=list,
+        description="逐文件 OCR 结果。",
+    )