refactor: Organize mail, stripe, gift, and Claude authentication modules into a new core package and update imports.

config.py

@@ -58,7 +58,7 @@ ADMIN_USERS: set[int] = {
 
 def get_merged_permissions() -> dict[int, set[str]]:
     """合并 config.toml 静态权限 + permissions.json 运行时权限"""
-    import permissions as perm_mod
+    from core import permissions as perm_mod
     merged = dict(_STATIC_PERMISSIONS)
     for uid, cmds in perm_mod.get_permissions_map().items():
         merged.setdefault(uid, set()).update(cmds)
@@ -73,4 +73,4 @@ MAIL_SYSTEMS: list[dict] = _cfg.get("mail", [])
 
 # --- 代理池 ---
 # 代理逻辑统一由 proxy_pool.py 管理，这里只做 re-export 保持兼容
-from proxy_pool import get_proxy, get_proxy_count  # noqa: E402, F401
+from core.proxy_pool import get_proxy, get_proxy_count  # noqa: E402, F401