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/scripts/bootstrap_paddleocr_mobile.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+OCR_VENV_DIR="${ROOT_DIR}/.venv-ocr312"
+PYTHON_BIN="${PYTHON_BIN:-python3.12}"
+
+if ! command -v "${PYTHON_BIN}" >/dev/null 2>&1; then
+  echo "python3.12 不存在，请先安装 Python 3.12。" >&2
+  exit 1
+fi
+
+apt-get update
+apt-get install -y libgl1 libglib2.0-0
+
+"${PYTHON_BIN}" -m venv "${OCR_VENV_DIR}"
+"${OCR_VENV_DIR}/bin/pip" install --upgrade pip
+"${OCR_VENV_DIR}/bin/pip" install "paddlepaddle==3.2.0" "paddleocr==3.5.0"
+
+echo "PaddleOCR mobile runtime 已安装到 ${OCR_VENV_DIR}"