feat: 添加 Agent 步骤事件与图片附件功能

- 新增 stepStarted/stepFinished 事件类型支持
- 前端实现图片附件上传和预览功能
- 后端增强工具结果存储和事件处理
- 完善相关单元测试和集成测试

backend/tests/unit/services/base/test_supabase_service.py

@@ -67,10 +67,8 @@ async def test_close_clears_clients(monkeypatch: pytest.MonkeyPatch) -> None:
     assert await service.initialize() is True
     assert await service.close() is True
     assert service.is_initialized is False
-    with pytest.raises(RuntimeError):
-        service.get_client()
-    with pytest.raises(RuntimeError):
-        service.get_admin_client()
+    assert service.get_client() is not None
+    assert service.get_admin_client() is not None
 
 
 @pytest.mark.asyncio
@@ -117,7 +115,47 @@ def test_get_client_raises_before_init() -> None:
         settings=SupabaseSettings(public_url="https://test.supabase.co")
     )
 
+    assert service.get_client() is not None
+    assert service.get_admin_client() is not None
+
+
+def test_get_client_raises_when_lazy_initialization_fails(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    service = SupabaseService(
+        settings=SupabaseSettings(public_url="https://test.supabase.co")
+    )
+
+    def _fake_create_client(_: str, __: str) -> object:
+        raise RuntimeError("boom")
+
+    monkeypatch.setattr("services.base.supabase.create_client", _fake_create_client)
+
     with pytest.raises(RuntimeError):
         service.get_client()
     with pytest.raises(RuntimeError):
         service.get_admin_client()
+
+
+def test_get_admin_client_lazily_initializes_clients(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    service = SupabaseService(
+        settings=SupabaseSettings(public_url="https://test.supabase.co")
+    )
+    anon_client = MagicMock(name="anon")
+    admin_client = MagicMock(name="admin")
+    create_calls: list[tuple[str, str]] = []
+
+    def _fake_create_client(url: str, key: str) -> object:
+        create_calls.append((url, key))
+        return anon_client if len(create_calls) == 1 else admin_client
+
+    monkeypatch.setattr("services.base.supabase.create_client", _fake_create_client)
+
+    resolved_admin = service.get_admin_client()
+
+    assert resolved_admin is admin_client
+    assert service.get_client() is anon_client
+    assert service.is_initialized is True
+    assert len(create_calls) == 2