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/schemas/agent/runtime_models.py

@@ -312,13 +312,12 @@ class ToolAgentOutput(BaseModel):
         description="Snapshot of tool call arguments for traceability and debugging.",
     )
     status: ToolStatus = Field(..., description="Tool execution status.")
-    result_summary: str = Field(
+    result: str = Field(
         ...,
-        description="Concise tool result summary with key facts and without verbose logs.",
-    )
-    ui_hints: UiHintsPayload | None = Field(
-        default=None,
-        description="Optional UI semantic hints translated into ui_schema by ui_compiler.",
+        description=(
+            "Compact machine-oriented tool result. Keep it short but include "
+            "action-critical facts (ids/status/counts) for downstream agent steps."
+        ),
     )
     error: ErrorInfo | None = Field(
         default=None, description="Tool execution error details."