feat(family): an idea links to the rule topic holding its norms - set_family_topic, the readouts name the rules, the idea row shows the link (milestone 463 step 1 gap, found in step 7, #4993)

Step 1 added family_ideas.topic_id but nothing could set it, so the note<->topic
link the milestone promised existed only as a column. set_family_topic links or
unlinks (0) a topic in a rulebook the caller owns, one idea per topic; the
version does not move. get_family_idea and get_family_adoption list the topic's
rules; list_family_ideas and the Family page name the topic. The model
docstrings no longer claim the topic's rules are platform-scoped in retrieval.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/scribe/mcp/server.py

@@ -196,7 +196,7 @@ _WRITE_TOOLS = frozenset({
     "undo_family_decision",
     # family canon — the adoption ledger
     "revise_family_idea", "assess_family_adoption", "resolve_family_conflict",
-    "set_family_references",
+    "set_family_references", "set_family_topic",
     "bind_repo", "unbind_repo",
     # snippets, processes, the shape ledger
     "create_snippet", "update_snippet", "delete_snippet", "verify_snippet",