feat: 新增可配置的路径前缀以支持子路径部署

添加前后端环境变量配置示例，新增后端路径前缀配置项，更新后端路由与静态文件挂载逻辑，调整前端代理配置与 API 调用代码，适配子路径部署场景。

backend/app/main.py

@@ -48,6 +48,14 @@ app = FastAPI(
     lifespan=lifespan,
 )
 
+api_prefix = settings.api_prefix.rstrip("/") or ""
+if api_prefix and not api_prefix.startswith("/"):
+    api_prefix = f"/{api_prefix}"
+
+uploads_prefix = settings.uploads_prefix.rstrip("/") or ""
+if uploads_prefix and not uploads_prefix.startswith("/"):
+    uploads_prefix = f"/{uploads_prefix}"
+
 # CORS 配置
 cors_origins = (
     ["*"]
@@ -88,20 +96,20 @@ async def global_exception_handler(request: Request, exc: Exception):
         content={"detail": "服务器内部错误，请稍后重试"},
     )
 
-app.mount("/uploads", StaticFiles(directory=settings.upload_dir), name="uploads")
+app.mount(uploads_prefix or "/uploads", StaticFiles(directory=settings.upload_dir), name="uploads")
 
-app.include_router(auth.router, prefix="/api/auth", tags=["认证"])
-app.include_router(user.router, prefix="/api/user", tags=["用户"])
-app.include_router(report.router, prefix="/api/report", tags=["报告"])
-app.include_router(analysis.router, prefix="/api/analysis", tags=["AI解读"])
-app.include_router(chat.router, prefix="/api/chat", tags=["AI对话"])
-app.include_router(health_records.router, prefix="/api/health-records", tags=["健康档案"])
-app.include_router(calendar.router, prefix="/api/calendar", tags=["产检日历"])
-app.include_router(doctor.router, prefix="/api/doctor", tags=["专家咨询"])
-app.include_router(share.router, prefix="/api/share", tags=["分享"])
+app.include_router(auth.router, prefix=f"{api_prefix}/auth", tags=["认证"])
+app.include_router(user.router, prefix=f"{api_prefix}/user", tags=["用户"])
+app.include_router(report.router, prefix=f"{api_prefix}/report", tags=["报告"])
+app.include_router(analysis.router, prefix=f"{api_prefix}/analysis", tags=["AI解读"])
+app.include_router(chat.router, prefix=f"{api_prefix}/chat", tags=["AI对话"])
+app.include_router(health_records.router, prefix=f"{api_prefix}/health-records", tags=["健康档案"])
+app.include_router(calendar.router, prefix=f"{api_prefix}/calendar", tags=["产检日历"])
+app.include_router(doctor.router, prefix=f"{api_prefix}/doctor", tags=["专家咨询"])
+app.include_router(share.router, prefix=f"{api_prefix}/share", tags=["分享"])
 
 
-@app.get("/api/health")
+@app.get(f"{api_prefix}/health")
 async def health_check():
     return {"status": "ok", "service": "孕育无忧 API"}