feat: Provider 异步删除、可配置密码策略、Hub 超时优化及多项改进

- 新增 Provider 异步删除任务系统，后台分阶段删除子资源并清理残留引用
- 新增可配置密码策略等级（weak/medium/strong），支持系统设置面板调整
- aether-hub 升级至 0.1.4，idle timeout 支持禁用（设为 0），worker 默认超时调整为 120s
- OAuth 手动续期增加 Redis 分布式锁，防止并发刷新冲突
- ProxyNode 心跳检测改为 asyncio.to_thread，避免阻塞事件循环
- 删除 ModelMultiSelect 和 useInvalidModels，MultiSelect 组件通用化
- 明确 allowed_providers/allowed_api_formats 的 NULL 与空数组语义
- 前端 StandaloneKeyFormDialog、UserFormDialog 等多处 UI 优化
- 新增 Alembic 迁移脚本清理 Provider 删除后的残留引用
- 补充相关测试用例

tests/unit/test_password_policy.py

@@ -0,0 +1,54 @@
+import pytest
+
+from src.core.validators import PasswordPolicyLevel, PasswordValidator
+
+
+class TestPasswordPolicy:
+    def test_default_policy_is_weak(self) -> None:
+        valid, error = PasswordValidator.validate("123456")
+
+        assert valid is True
+        assert error is None
+
+    @pytest.mark.parametrize(
+        ("password", "expected_error"),
+        [
+            ("1234567", "密码长度至少为8个字符"),
+            ("12345678", "密码必须包含至少一个字母"),
+            ("abcdefgh", "密码必须包含至少一个数字"),
+        ],
+    )
+    def test_medium_policy_rejects_weak_patterns(self, password: str, expected_error: str) -> None:
+        valid, error = PasswordValidator.validate(password, policy=PasswordPolicyLevel.MEDIUM)
+
+        assert valid is False
+        assert error == expected_error
+
+    def test_medium_policy_accepts_letters_and_digits(self) -> None:
+        valid, error = PasswordValidator.validate("abc12345", policy=PasswordPolicyLevel.MEDIUM)
+
+        assert valid is True
+        assert error is None
+
+    @pytest.mark.parametrize(
+        ("password", "expected_error"),
+        [
+            ("abc12345", "密码必须包含至少一个大写字母"),
+            ("ABC12345", "密码必须包含至少一个小写字母"),
+            ("Abcdefgh", "密码必须包含至少一个数字"),
+            ("Abcd1234", "密码必须包含至少一个特殊字符"),
+        ],
+    )
+    def test_strong_policy_requires_upper_lower_and_digit(
+        self, password: str, expected_error: str
+    ) -> None:
+        valid, error = PasswordValidator.validate(password, policy=PasswordPolicyLevel.STRONG)
+
+        assert valid is False
+        assert error == expected_error
+
+    def test_strong_policy_accepts_mixed_password(self) -> None:
+        valid, error = PasswordValidator.validate("Abcd1234!", policy="strong")
+
+        assert valid is True
+        assert error is None