feat(mcp): scaffold in-app FastMCP package

Empty FastMCP instance with the post-pivot instructions block. Tools
get registered in phases 2 and 3; ASGI mounting + bearer-auth comes
in task 1.4.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/fabledassistant/mcp/__init__.py

@@ -0,0 +1,8 @@
+"""In-app MCP server. Exposes Fabled Scribe data via the MCP streamable-HTTP transport.
+
+Auth uses the existing `api_keys` table: a Bearer token in the Authorization
+header resolves to a user, and every tool call acts on that user's data only.
+"""
+from fabledassistant.mcp.server import build_mcp_server, mount_mcp
+
+__all__ = ["build_mcp_server", "mount_mcp"]

src/fabledassistant/mcp/server.py

@@ -0,0 +1,38 @@
+"""FastMCP instance + Quart mount-point. Tools are registered in mcp/tools/."""
+from __future__ import annotations
+
+from mcp.server.fastmcp import FastMCP
+from quart import Quart
+
+_INSTRUCTIONS = """
+Fabled Scribe is the user's self-hosted second-brain and project-management
+data store. You (Claude) are the assistant.
+
+Hierarchy: Project -> Milestone -> Task/Note.
+
+- Notes and Tasks share a model; tasks are notes with is_task=True.
+- Use fable_*_note tools for notes, fable_*_task tools for tasks.
+- Typed entities (person, place, list) are notes with a type field plus
+  type-specific columns; use the dedicated tools for those.
+- Tags are plain strings (no `#` prefix). Empty list clears tags; omit to leave
+  unchanged on updates.
+- For optional integer FKs (project_id, milestone_id, parent_id), use 0 to mean
+  "not set".
+"""
+
+
+def build_mcp_server() -> FastMCP:
+    """Build the FastMCP instance with all tools registered."""
+    mcp = FastMCP("fable", instructions=_INSTRUCTIONS.strip())
+    # Tools will be registered here in Phase 2/3.
+    return mcp
+
+
+def mount_mcp(app: Quart) -> None:
+    """Mount the FastMCP streamable-HTTP ASGI sub-app at /mcp on the Quart app.
+
+    Phase 1.2 scaffold: just builds and exposes the instance for tests. The
+    actual ASGI wiring with bearer-auth happens in Task 1.4.
+    """
+    mcp = build_mcp_server()
+    app.mcp_instance = mcp