feat(client): 添加 Python 客户端及示例应用

- 新增 python-client 模块，提供 ConfigClient 配置拉取、定时同步、变更监听
- 使用 pyaes 替代 cryptography 实现 AES 解密，避免编译问题
- 新增 python-client-demo Flask 示例应用
- .gitignore 添加 Python 相关忽略规则

python-client/kenaito_conf/cache.py

@@ -0,0 +1,22 @@
+import json
+import os
+
+CACHE_FILE = "config-cache.json"
+
+
+class Cache:
+    def __init__(self, cache_dir: str = "."):
+        self.cache_dir = cache_dir
+
+    def write(self, data: dict) -> None:
+        path = os.path.join(self.cache_dir, CACHE_FILE)
+        with open(path, "w", encoding="utf-8") as f:
+            json.dump(data, f, ensure_ascii=False)
+
+    def read(self) -> dict | None:
+        path = os.path.join(self.cache_dir, CACHE_FILE)
+        try:
+            with open(path, "r", encoding="utf-8") as f:
+                return json.load(f)
+        except (FileNotFoundError, json.JSONDecodeError):
+            return None