refactor: 重构 Tool Result 契约，移除 ui_hints 统一使用 result 字段

- ToolAgentOutput 移除 result_summary 和 ui_hints，统一使用 result 字段
- 日历/用户查找工具移除 ui_hints 输出，改为机器可读的结构化结果
- Agent History 移除 tool 消息的 ui_hints 处理逻辑
- App 版本检查改为 manifest.json 方式，支持多渠道发布
- 更新 settings 配置和测试用例适配新结构

backend/src/core/config/settings.py

@@ -199,23 +199,39 @@ class DatabaseSettings(BaseModel):
 
 
 class AppVersionSettings(BaseModel):
-    releases_dir: str = Field(
+    manifest_path: str = Field(
+        default="deploy/static/releases/manifest.json",
+        description="发布清单文件路径，相对于项目根目录",
+    )
+    release_path_prefix: str = Field(
         default="releases",
-        description="安装包目录，相对于项目根目录",
+        description="下载 URL 中文件目录前缀",
     )
-    current_version: str = Field(
-        default="0.1.0",
-        description="当前版本号",
-    )
-    current_build: int = Field(
-        default=1,
-        description="当前构建号",
-    )
-    download_base_url: str = Field(
-        default="",
+    download_base_url: AnyHttpUrl | None = Field(
+        default=None,
         description="下载链接基础域名，如 https://your-domain.com",
     )
 
+    @field_validator("download_base_url", mode="before")
+    @classmethod
+    def empty_download_base_url_to_none(cls, value: object) -> object:
+        if value == "":
+            return None
+        return value
+
+    @field_validator("manifest_path")
+    @classmethod
+    def validate_manifest_path(cls, value: str) -> str:
+        normalized = Path(value)
+        if normalized.is_absolute() or ".." in normalized.parts:
+            raise ValueError("manifest_path must be a safe relative path")
+        return value
+
+
+class TestSettings(BaseModel):
+    email: str = ""
+    password: str = ""
+
 
 def _resolve_env_file() -> str:
     current = Path(__file__).resolve()
@@ -241,6 +257,7 @@ class Settings(BaseSettings):
     taskiq: TaskiqSettings = TaskiqSettings()
     database: DatabaseSettings = DatabaseSettings()
     app_version: AppVersionSettings = AppVersionSettings()
+    test: TestSettings = Field(default_factory=TestSettings)
 
     @computed_field
     @property