feat(web): add THS stock associations API

pyproject.toml

@@ -16,7 +16,7 @@ easy-tdx = "easy_tdx.cli:cli"  # cli/__init__.py exposes the click group
 [project.optional-dependencies]
 dev = ["pytest>=8.0", "pytest-asyncio>=0.23", "pytest-cov", "mypy>=1.9", "ruff>=0.4", "scipy>=1.10,<1.16", "httpx>=0.27"]
 science = ["scipy>=1.10,<1.16"]
-web = ["fastapi>=0.110,<1", "uvicorn[standard]>=0.29"]
+web = ["fastapi>=0.110,<1", "uvicorn[standard]>=0.29", "httpx>=0.27"]
 # 打包成桌面 EXE 用：系统托盘（pystray）+ 图标生成（Pillow）。
 # 仅 PyInstaller 打包态需要，开发态 ``pip install -e .[web]`` 不强制装。
 packaging = ["pystray>=0.19", "Pillow>=10.0"]