streamable-httpトランスポート対応を追加

MCP SDK 2.xのMCPServer.run(transport="streamable-http")を使い、stdioに
加えてStreamable HTTPトランスポートで起動できるようにする。SSEはMCP仕様で
非推奨のため選択肢から除外し、transport enumはstdioとstreamable-httpの
2種類のみとした。

transportの選択はTOML [server] tableで指定し、CLI引数は追加しない。
仕様の「CLI上書きを行わない」「TOML集約」原則に準拠する。[server]省略時は
stdio（後方互換）、streamable-http時はhost=127.0.0.1 port=8000を既定値とする。

変更内容:
- config.py: ServerConfig dataclass、VALID_TRANSPORTS定数、AppConfig.server
  フィールド、load_configの[server]読込・validation追加
- cli.py: main()でconfig.server.transportに応じたrun()引数分岐
- tests/conftest.py: app_config fixtureにserver=ServerConfig()追加
- tests/test_config.py: [server]の正常系・異常系・境界値テスト追加
  (省略時stdio既定値、streamable-http読込、sse/http/ws/unknown拒否、
   port境界値0/65536/-1/文字列、host空文字拒否)
- doc/config.md: [server]セクション追記、設定項目一覧表更新
- config.example.toml: [server]コメント例追記
- doc/Specifications.md: スコープ表にMCPトランスポート行追加
- doc/Design.md: 責務表と起動フロー更新
- doc/mcp.md: 概要のtransport記載更新
- README.md: streamable-http起動例追記
- script/smoke_streamable_http.py: streamable-http経由の検証スクリプト追加

検証:
- ruff format/check、pyright 0 errors、pytest 50 passed
- 実GPU・実モデルでstreamable-http経由generate_imageの全ルート確認
  (HTTP接続→MCP initialize→tools/list→tools/call→PNG生成・返却)
- 生成結果: 335KB PNG、512x512、20 steps、CFG 7.0

2 files changed, 74 insertions, 0 deletions

diff --git a/tests/conftest.py b/tests/conftest.py
index d364dbd..862b4f5 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -14,6 +14,7 @@ from mcp_sd15.config import (
     GenerationConfig,
     ModelConfig,
     OutputConfig,
+    ServerConfig,
 )
 
 
@@ -28,6 +29,7 @@ def app_config(tmp_path: Path) -> AppConfig:
             inpaint=ControlModelConfig(True, "inpaint.safetensors"),
         ),
         output=OutputConfig(tmp_path / "outputs", False),
+        server=ServerConfig(),
     )
 
 
diff --git a/tests/test_config.py b/tests/test_config.py
index c24064b..9a6bf89 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -123,3 +123,75 @@ def test_can_skip_path_checks_for_schema_only_use(tmp_path: Path) -> None:
     config = load_config(path, validate_paths=False)
     assert config.model.root == (tmp_path / "missing").resolve()
     assert config.generation.scheduler == "dpmpp_2m_karras"
+
+
+def test_server_defaults_to_stdio_when_omitted(tmp_path: Path) -> None:
+    path = tmp_path / "config.toml"
+    path.write_text(
+        f'[model]\nroot = "{tmp_path.as_posix()}"\ncheckpoint = "base.safetensors"\n',
+        encoding="utf-8",
+    )
+    config = load_config(path, validate_paths=False)
+    assert config.server.transport == "stdio"
+    assert config.server.host == "127.0.0.1"
+    assert config.server.port == 8000
+
+
+def test_server_reads_streamable_http(tmp_path: Path) -> None:
+    path = tmp_path / "config.toml"
+    path.write_text(
+        f'[model]\nroot = "{tmp_path.as_posix()}"\ncheckpoint = "base.safetensors"\n'
+        '[server]\ntransport = "streamable-http"\nhost = "0.0.0.0"\nport = 9000\n',
+        encoding="utf-8",
+    )
+    config = load_config(path, validate_paths=False)
+    assert config.server.transport == "streamable-http"
+    assert config.server.host == "0.0.0.0"
+    assert config.server.port == 9000
+
+
+@pytest.mark.parametrize(
+    "transport",
+    ["sse", "http", "ws", "unknown"],
+)
+def test_rejects_invalid_transport(tmp_path: Path, transport: str) -> None:
+    path = tmp_path / "config.toml"
+    path.write_text(
+        f'[model]\nroot = "{tmp_path.as_posix()}"\ncheckpoint = "base.safetensors"\n'
+        f'[server]\ntransport = "{transport}"\n',
+        encoding="utf-8",
+    )
+    with pytest.raises(ConfigError, match="transport"):
+        load_config(path, validate_paths=False)
+
+
+@pytest.mark.parametrize(
+    "port, message",
+    [
+        (0, "port"),
+        (65536, "port"),
+        (-1, "port"),
+        ("8000", "port"),
+    ],
+)
+def test_rejects_invalid_port(tmp_path: Path, port: str | int, message: str) -> None:
+    path = tmp_path / "config.toml"
+    port_literal = f'"{port}"' if isinstance(port, str) else str(port)
+    path.write_text(
+        f'[model]\nroot = "{tmp_path.as_posix()}"\ncheckpoint = "base.safetensors"\n'
+        f'[server]\ntransport = "streamable-http"\nport = {port_literal}\n',
+        encoding="utf-8",
+    )
+    with pytest.raises(ConfigError, match=message):
+        load_config(path, validate_paths=False)
+
+
+def test_rejects_empty_host(tmp_path: Path) -> None:
+    path = tmp_path / "config.toml"
+    path.write_text(
+        f'[model]\nroot = "{tmp_path.as_posix()}"\ncheckpoint = "base.safetensors"\n'
+        '[server]\ntransport = "streamable-http"\nhost = ""\n',
+        encoding="utf-8",
+    )
+    with pytest.raises(ConfigError, match="host"):
+        load_config(path, validate_paths=False)