feat: MCP Server plugin (Task 5.16) - expose LeoCRM tools to external AI clients

- New plugin app/plugins/builtins/mcp_server/ with 9 MCP tools
- Tools: search_contacts, get_contact, create_contact, list_calendar_entries,
  create_calendar_entry, list_emails, send_email, list_files, upload_file
- Routes: GET /api/v1/mcp/tools, POST /api/v1/mcp/tools/{name}/execute, GET /api/v1/mcp/config
- API-token auth via session + RBAC (mcp:read, mcp:write)
- Frontend: mcp.ts API client with React Query hooks
- Frontend: SettingsMcp.tsx settings page with tool listing and execution
- i18n: de.json and en.json updated with MCP entries
- Tests: 7 tests covering tool listing, config, execution, auth, schema validation

tests/conftest.py

@@ -38,6 +38,9 @@ from app.models.user import User, UserTenant
 from app.models.user_preference import UserPreference  # noqa: F401
 from app.models.workflow import Workflow, WorkflowInstance, WorkflowStepHistory  # noqa: F401
 from app.plugins.builtins.calendar import CalendarPlugin  # noqa: F401
+from app.plugins.builtins.mcp_server import McpServerPlugin  # noqa: F401
+from app.plugins.builtins.mcp_client import McpClientPlugin  # noqa: F401
+from app.plugins.builtins.mcp_client.models import McpServerConfig  # noqa: F401
 from app.plugins.builtins.calendar.models import (  # noqa: F401
     Calendar,
     CalendarEntry,
@@ -434,3 +437,61 @@ async def calendar_authed_client(
     assert resp.status_code == 200, f"Calendar activate failed: {resp.text}"
 
     return calendar_client, seed
+
+
+# ─── MCP Server / Client Fixtures ───────────────────────────────────────────
+
+@pytest_asyncio.fixture
+async def mcp_app(engine: AsyncEngine, redis_client):
+    """FastAPI app with MCP Server + Client + Permissions plugins registered, installed, and activated."""
+    reset_engine_for_testing(engine)
+    app = create_app()
+
+    registry = reset_registry_for_testing()
+    registry.initialize(engine, app)
+
+    container = get_container()
+    await container.initialize()
+
+    registry.register_plugin(PermissionsPlugin())
+    registry.register_plugin(McpServerPlugin())
+    registry.register_plugin(McpClientPlugin())
+    reset_plugin_service_for_testing(registry)
+
+    _sf = async_sessionmaker(bind=engine, expire_on_commit=False, class_=AsyncSession)
+    async with _sf() as session:
+        await registry.install(session, "permissions")
+        await registry.activate(session, "permissions")
+        await registry.install(session, "mcp_server")
+        await registry.activate(session, "mcp_server")
+        await registry.install(session, "mcp_client")
+        await registry.activate(session, "mcp_client")
+        await session.commit()
+
+    yield app
+    await close_engine()
+
+
+@pytest_asyncio.fixture
+async def mcp_client_fixture(mcp_app) -> AsyncClient:
+    transport = ASGITransport(app=mcp_app)
+    async with AsyncClient(transport=transport, base_url="http://test") as c:
+        yield c
+
+
+@pytest_asyncio.fixture
+async def mcp_authed_client(
+    mcp_client_fixture: AsyncClient, db_session: AsyncSession
+) -> tuple[AsyncClient, dict]:
+    """Authenticated admin client with seeded data and MCP plugins activated."""
+    seed = await seed_tenant_and_users(db_session)
+    login_resp = await mcp_client_fixture.post(
+        "/api/v1/auth/login",
+        json={"email": "admin@tenanta.com", "password": "TestPass123!"},
+        headers=ORIGIN_HEADER,
+    )
+    assert login_resp.status_code == 200, f"Login failed: {login_resp.text}"
+    csrf_token = login_resp.json().get("csrf_token", "")
+    mcp_client_fixture.headers.update({"X-CSRF-Token": csrf_token})
+
+    return mcp_client_fixture, seed