feat: scaffold fable-mcp Python package

pyproject.toml with mcp[cli]/httpx/python-dotenv deps, entry point
fable-mcp=fable_mcp.server:main, dev deps for testing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fable-mcp/tests/conftest.py

@@ -0,0 +1,12 @@
+"""Shared pytest fixtures for fable-mcp tests."""
+from unittest.mock import AsyncMock, MagicMock
+import pytest
+
+
+@pytest.fixture
+def mock_client():
+    """A mock FableClient that returns empty responses by default."""
+    client = AsyncMock()
+    client.__aenter__ = AsyncMock(return_value=client)
+    client.__aexit__ = AsyncMock(return_value=False)
+    return client