feat(fable-mcp): implement FableClient, all tool modules, and server.py

- client.py: async httpx wrapper, FableAPIError, stream_get() SSE generator,
  singleton init_client()/get_client() and _reset_client() for tests
- tools/: notes, tasks, projects, milestones, search, chat — thin async
  functions that accept FableClient and call Fable REST endpoints
- server.py: FastMCP entry point with 20 tools registered via @mcp.tool(),
  each opening a fresh FableClient context per call; validates env vars at startup
- tests: 34 tests covering client HTTP behaviour, error handling, singleton,
  SSE streaming, and all tool modules

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

fable-mcp/tests/test_tools_projects.py

@@ -0,0 +1,42 @@
+"""Tests for projects MCP tools."""
+import pytest
+from unittest.mock import AsyncMock
+
+
+@pytest.fixture
+def client(mock_client):
+    return mock_client
+
+
+@pytest.mark.asyncio
+async def test_list_projects_calls_get(client):
+    from fable_mcp.tools.projects import list_projects
+    client.get = AsyncMock(return_value={"projects": []})
+    await list_projects(client)
+    client.get.assert_called_once_with("/api/projects")
+
+
+@pytest.mark.asyncio
+async def test_get_project_calls_correct_endpoint(client):
+    from fable_mcp.tools.projects import get_project
+    client.get = AsyncMock(return_value={"id": 2, "title": "Proj"})
+    result = await get_project(client, project_id=2)
+    client.get.assert_called_once_with("/api/projects/2")
+
+
+@pytest.mark.asyncio
+async def test_create_project_posts_payload(client):
+    from fable_mcp.tools.projects import create_project
+    client.post = AsyncMock(return_value={"id": 4, "title": "New"})
+    await create_project(client, title="New", description="Desc")
+    call_kwargs = client.post.call_args[1]
+    assert call_kwargs["json"]["title"] == "New"
+    assert call_kwargs["json"]["description"] == "Desc"
+
+
+@pytest.mark.asyncio
+async def test_update_project_patches(client):
+    from fable_mcp.tools.projects import update_project
+    client.patch = AsyncMock(return_value={"id": 4, "status": "active"})
+    await update_project(client, project_id=4, status="active")
+    assert "/api/projects/4" in client.patch.call_args[0][0]