feat(rules): move a rule between global and project scope, keeping its id, history, areas and edges (#4063)

A rule's home is its reach: a rulebook topic makes it global, a project makes it
that project's. There was no way to change one, so a project rule decided to be
global could only be recreated and the original trashed — losing the id every
record cites, its edit history, its area tags and its relations.

- services.rulebooks.move_rule(rule_id, user_id, topic_id= | project_id=):
  exactly one destination (the model's CHECK), owned by the caller, not the
  rule's current home. A topic already holding a live rule with the same title
  is refused with a message naming that rule, instead of uq_rule_per_topic
  failing the commit. Someone else's rule reads as not found.
- Deliberately NOT done, and said in the docstring: no version (a version is
  what a rule said, milestone 323 decision 4), no duplicate gate (nothing new
  enters the corpus), no re-embed (retrieval reads the home at query time).
- Both doors: MCP move_rule, REST POST /api/rules/<id>/move (rule 33).
- UI: RuleHomePicker, one component in the rule editor (a global rule) and a
  project's rules tab (a project rule), so the two cannot drift on what a
  destination is.
- using-scribe names move_rule under "Where a new rule goes". Plugin
  2026.09.15.1626.

Milestone 414 step 3.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

src/scribe/routes/rulebooks.py

@@ -297,6 +297,27 @@ async def unrelate_rules(relation_id: int):
     return "", 204
 
 
+@rulebooks_bp.post("/rules/<int:rule_id>/move")
+@login_required
+async def move_rule(rule_id: int):
+    """Give a rule a new home: {topic_id} makes it global, {project_id} makes
+    it that project's. The MCP twin is move_rule (rule 33: same names)."""
+    data = await request.get_json() or {}
+    uid = get_current_user_id()
+    try:
+        rule = await rulebooks_svc.move_rule(
+            rule_id, uid,
+            topic_id=int(data.get("topic_id") or 0),
+            project_id=int(data.get("project_id") or 0),
+        )
+    except (TypeError, ValueError) as exc:
+        msg = str(exc)
+        return jsonify({"error": msg}), 404 if "not found" in msg else 400
+    if rule is None:
+        return jsonify({"error": "rule not found"}), 404
+    return jsonify(await rulebooks_svc.rule_detail(uid, rule))
+
+
 @rulebooks_bp.delete("/rules/<int:rule_id>")
 @login_required
 async def delete_rule(rule_id: int):