feat(mcp): task CRUD tools + add_task_log

Five tools wrapping services/notes.py with is_task=True (tasks are
notes with non-null status) plus services/task_logs.create_log for
add_task_log. Matches existing fable-mcp contracts. No delete_task —
preserves existing surface; cancel by updating status to "cancelled".

fable_get_task enriches with parent_title (extra service call when
parent_id is set), matching the existing route's behavior.

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

src/fabledassistant/mcp/tools/__init__.py

@@ -4,10 +4,11 @@ Each tool module exposes a `register(mcp)` function that attaches its tools
 to a FastMCP instance. `register_all(mcp)` is the single entry point called
 from `mcp.server.build_mcp_server`.
 """
-from fabledassistant.mcp.tools import notes, search
+from fabledassistant.mcp.tools import notes, search, tasks
 
 
 def register_all(mcp) -> None:
     """Register every tool module's tools on the given FastMCP instance."""
     search.register(mcp)
     notes.register(mcp)
+    tasks.register(mcp)