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/api/v1/endpoints/ocr.py

@@ -0,0 +1,56 @@
+from __future__ import annotations
+
+from typing import Annotated
+
+from fastapi import APIRouter, Depends, File, HTTPException, UploadFile, status
+
+from app.api.deps import CurrentUserContext, get_current_user
+from app.schemas.common import ErrorResponse
+from app.schemas.ocr import OcrRecognizeBatchRead
+from app.services.ocr import OcrService
+
+router = APIRouter(prefix="/ocr")
+
+
+@router.post(
+    "/recognize",
+    response_model=OcrRecognizeBatchRead,
+    summary="识别票据或图片 OCR",
+    description="使用 PaddleOCR mobile 模型对上传的图片或 PDF 执行 OCR，并返回结构化文本摘要。",
+    responses={
+        status.HTTP_400_BAD_REQUEST: {
+            "model": ErrorResponse,
+            "description": "未上传文件或文件参数非法。",
+        },
+        status.HTTP_401_UNAUTHORIZED: {
+            "model": ErrorResponse,
+            "description": "未提供当前登录用户。",
+        },
+        status.HTTP_503_SERVICE_UNAVAILABLE: {
+            "model": ErrorResponse,
+            "description": "OCR 运行时不可用或执行失败。",
+        },
+    },
+)
+async def recognize_ocr_documents(
+    files: Annotated[list[UploadFile], File(description="待识别的票据图片或 PDF。")],
+    _: Annotated[CurrentUserContext, Depends(get_current_user)],
+) -> OcrRecognizeBatchRead:
+    try:
+        payload = []
+        for upload in files:
+            payload.append(
+                (
+                    str(upload.filename or "upload.bin"),
+                    await upload.read(),
+                    upload.content_type,
+                )
+            )
+        return OcrService().recognize_files(payload)
+    except ValueError as exc:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail=str(exc)) from exc
+    except RuntimeError as exc:
+        raise HTTPException(
+            status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
+            detail=str(exc),
+        ) from exc