feat(server): 平台默认组合——Windows granian+winloop，Unix granian+rloop

- granian[reload,rloop,uvloop,winloop] 改为默认依赖，uv sync 即具备完整启动栈
- auto 在启动器内解析为具体循环：granian Windows→winloop / Unix→rloop（缺省回退 uvloop/asyncio）；
  uvicorn Unix→uvloop / Windows→asyncio
- 启动日志打印实际 server+loop；测试覆盖平台默认与回退；README 默认矩阵更新

tests/test_serve.py

@@ -45,11 +45,57 @@ def test_uvicorn_rejects_granian_only_loops() -> None:
         serve.resolve_loop("uvicorn", "rloop")
 
 
-def test_uvicorn_auto_and_asyncio_allowed() -> None:
-    assert serve.resolve_loop("uvicorn", "auto") == "auto"
+def test_uvicorn_auto_and_asyncio_allowed(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(serve, "IS_WINDOWS", True)
+    assert serve.resolve_loop("uvicorn", "auto") == "asyncio"
     assert serve.resolve_loop("uvicorn", "asyncio") == "asyncio"
 
 
+def test_default_loop_granian_windows(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(serve, "IS_WINDOWS", True)
+    monkeypatch.setattr(serve, "has_module", lambda name: name == "winloop")
+    assert serve.default_loop("granian") == "winloop"
+
+
+def test_default_loop_granian_unix_prefers_rloop(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(serve, "IS_WINDOWS", False)
+    monkeypatch.setattr(serve, "has_module", lambda name: name in ("rloop", "uvloop"))
+    assert serve.default_loop("granian") == "rloop"
+
+
+def test_default_loop_granian_unix_falls_back(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(serve, "IS_WINDOWS", False)
+    monkeypatch.setattr(serve, "has_module", lambda name: name == "uvloop")
+    assert serve.default_loop("granian") == "uvloop"
+
+    monkeypatch.setattr(serve, "has_module", lambda name: False)
+    assert serve.default_loop("granian") == "asyncio"
+
+
+def test_default_loop_uvicorn(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(serve, "IS_WINDOWS", False)
+    monkeypatch.setattr(serve, "has_module", lambda name: name == "uvloop")
+    assert serve.default_loop("uvicorn") == "uvloop"
+
+    # Windows 上 uvicorn 只有 asyncio（即使装了 winloop 也不会用）
+    monkeypatch.setattr(serve, "IS_WINDOWS", True)
+    monkeypatch.setattr(serve, "has_module", lambda name: name == "winloop")
+    assert serve.default_loop("uvicorn") == "asyncio"
+
+
+def test_default_loop_windows_without_winloop(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(serve, "IS_WINDOWS", True)
+    monkeypatch.setattr(serve, "has_module", lambda name: False)
+    assert serve.default_loop("granian") == "asyncio"
+
+
+def test_resolve_loop_auto_uses_platform_default(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(serve, "IS_WINDOWS", False)
+    monkeypatch.setattr(serve, "has_module", lambda name: name in ("rloop", "uvloop"))
+    assert serve.resolve_loop("granian", "auto") == "rloop"
+    assert serve.resolve_loop("uvicorn", "auto") == "uvloop"
+
+
 def test_build_command_granian(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.setattr(serve, "has_module", lambda name: True)
     command = serve.build_command("granian", host="0.0.0.0", port=16688, workers=2, loop="winloop", reload=True)