feat(mcp): fable_list_tags + fable_get_recent

Two cross-type bootstrap tools:

- fable_list_tags: tag vocabulary with usage counts, top-N by count.
  Aggregation in Python (not SQL UNNEST) — trivial perf cost at
  personal scale, much easier to test.

- fable_get_recent: most-recently-touched items across notes, tasks,
  projects, events. Useful for Claude to ask 'what was I working on
  recently' at the start of a conversation.

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

src/fabledassistant/mcp/tools/__init__.py

@@ -5,7 +5,7 @@ to a FastMCP instance. `register_all(mcp)` is the single entry point called
 from `mcp.server.build_mcp_server`.
 """
 from fabledassistant.mcp.tools import (
-    events, milestones, notes, projects, search, tasks,
+    events, milestones, notes, projects, recent, search, tags, tasks,
 )
 
 
@@ -17,3 +17,5 @@ def register_all(mcp) -> None:
     projects.register(mcp)
     milestones.register(mcp)
     events.register(mcp)
+    tags.register(mcp)
+    recent.register(mcp)