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

frontend/src/stores/rulebooks.ts

@@ -137,6 +137,20 @@ export const useRulebooksStore = defineStore("rulebooks", () => {
     return rule;
   }
 
+  /** After a move (milestone 414): take the rule out of whichever topic list
+   *  held it, and into its new topic's list if that one is loaded. A rule moved
+   *  onto a project belongs to no topic list at all. */
+  function placeMovedRule(rule: Rule) {
+    if (currentRule.value?.id === rule.id) currentRule.value = rule;
+    for (const tid of Object.keys(rulesByTopic.value)) {
+      const key = Number(tid);
+      rulesByTopic.value[key] = rulesByTopic.value[key].filter((r) => r.id !== rule.id);
+    }
+    if (rule.topic_id !== null && rulesByTopic.value[rule.topic_id]) {
+      rulesByTopic.value[rule.topic_id].push(toHeader(rule));
+    }
+  }
+
   async function relateRules(
     fromRuleId: number,
     data: { to_rule_id: number; kind: api.RuleRelationKind; note?: string },
@@ -198,6 +212,7 @@ export const useRulebooksStore = defineStore("rulebooks", () => {
 
   return {
     rulebooks, topicsByRulebook, rulesByTopic, currentRule, rulesDue, lastSweepOpts, loading,
+    placeMovedRule,
     fetchRulebooks, fetchTopics, fetchRules, fetchRule,
     createRulebook, updateRulebook, deleteRulebook,
     createTopic, updateTopic, deleteTopic,