fix(env): 本机启动读取根目录 .env，监听地址兼容 BIND_ADDR

- study_tool/__init__.py 用 python-dotenv 加载根目录 .env，位置早于
  store / config 读环境变量；已有环境变量优先，Docker 注入的不受影响
- app.py 监听地址改为 HOST -> BIND_ADDR -> 127.0.0.1 依次回退
- 新增依赖 python-dotenv>=1.0（pyproject.toml / requirements.txt / uv.lock）
- README 环境变量表补充 .env 说明与 BIND_ADDR / TZ 两行
- CHANGELOG / docs/OPTIMIZATION.md 记录本次修复，版本号 0.0.6 -> 0.0.7

uv.lock

@@ -1380,6 +1380,15 @@ wheels = [
     { url = "https://mirrors.aliyun.com/pypi/packages/f7/5e/35c856e186b74678c24927847ad9895a51f1bc02a0c6126477a6c6040064/pyreadline3-3.5.6-py3-none-any.whl", hash = "sha256:8449b734232e42a5dcd74048e39b60db2839a4c38cf3ae2bf7707d58b5389c0d" },
 ]
 
+[[package]]
+name = "python-dotenv"
+version = "1.2.4"
+source = { registry = "https://mirrors.aliyun.com/pypi/simple" }
+sdist = { url = "https://mirrors.aliyun.com/pypi/packages/74/26/2fbeedb218a787a5eea551c7532cac4e009f83d689dd2faa0d0353473f86/python_dotenv-1.2.4.tar.gz", hash = "sha256:f0d53e69935a851c0dcc78f3ab7aaccd8cabef0b92382b576b824212902873c0" }
+wheels = [
+    { url = "https://mirrors.aliyun.com/pypi/packages/60/d1/38f3a3405989a89ac18390803e70c6ad7c7760da4f9b83cbeca0c44a0c72/python_dotenv-1.2.4-py3-none-any.whl", hash = "sha256:42269a8a5b3fd54ffa6f3d84b18abed50064717576b4ecf03dc4a55d8aa04fdc" },
+]
+
 [[package]]
 name = "requests"
 version = "2.34.2"
@@ -1465,6 +1474,7 @@ dependencies = [
     { name = "fastapi" },
     { name = "lxml" },
     { name = "playwright" },
+    { name = "python-dotenv" },
     { name = "requests" },
     { name = "uvicorn" },
 ]
@@ -1476,6 +1486,7 @@ requires-dist = [
     { name = "fastapi", specifier = ">=0.110" },
     { name = "lxml", specifier = ">=5.0" },
     { name = "playwright", specifier = ">=1.40" },
+    { name = "python-dotenv", specifier = ">=1.0" },
     { name = "requests", specifier = ">=2.31" },
     { name = "uvicorn", specifier = ">=0.27" },
 ]