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/fable_mcp/tools/notes.py

@@ -0,0 +1,72 @@
+"""MCP tools for Fable notes."""
+from __future__ import annotations
+
+from typing import Any
+
+from fable_mcp.client import FableClient
+
+
+async def list_notes(
+    client: FableClient,
+    *,
+    limit: int = 20,
+    offset: int = 0,
+    tag: str | None = None,
+    search: str | None = None,
+) -> dict[str, Any]:
+    """List notes with optional filtering."""
+    params: dict[str, Any] = {"limit": limit, "offset": offset}
+    if tag:
+        params["tag"] = tag
+    if search:
+        params["search"] = search
+    return await client.get("/api/notes", params=params)
+
+
+async def get_note(client: FableClient, *, note_id: int) -> dict[str, Any]:
+    """Fetch a single note by ID."""
+    return await client.get(f"/api/notes/{note_id}")
+
+
+async def create_note(
+    client: FableClient,
+    *,
+    title: str,
+    body: str = "",
+    tags: list[str] | None = None,
+    project_id: int | None = None,
+) -> dict[str, Any]:
+    """Create a new note."""
+    payload: dict[str, Any] = {"title": title, "body": body}
+    if tags is not None:
+        payload["tags"] = tags
+    if project_id is not None:
+        payload["project_id"] = project_id
+    return await client.post("/api/notes", json=payload)
+
+
+async def update_note(
+    client: FableClient,
+    *,
+    note_id: int,
+    title: str | None = None,
+    body: str | None = None,
+    tags: list[str] | None = None,
+    project_id: int | None = None,
+) -> dict[str, Any]:
+    """Update an existing note."""
+    payload: dict[str, Any] = {}
+    if title is not None:
+        payload["title"] = title
+    if body is not None:
+        payload["body"] = body
+    if tags is not None:
+        payload["tags"] = tags
+    if project_id is not None:
+        payload["project_id"] = project_id
+    return await client.patch(f"/api/notes/{note_id}", json=payload)
+
+
+async def delete_note(client: FableClient, *, note_id: int) -> None:
+    """Delete a note by ID."""
+    await client.delete(f"/api/notes/{note_id}")