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/components/rules/RuleEditorSlideOver.vue

@@ -3,6 +3,8 @@ import { computed, ref, watch, onMounted } from "vue";
 import { useRulebooksStore } from "@/stores/rulebooks";
 import { useCanonicalSystemsStore } from "@/stores/canonicalSystems";
 import RuleHistoryPanel from "@/components/rules/RuleHistoryPanel.vue";
+import RuleHomePicker from "@/components/rules/RuleHomePicker.vue";
+import type { Rule } from "@/api/rulebooks";
 
 const props = defineProps<{ ruleId: number | null; topicId: number | null }>();
 const emit = defineEmits<{ close: [] }>();
@@ -115,6 +117,14 @@ async function save() {
   emit("close");
 }
 
+// A moved rule has left the topic this view lists (or joined another). The
+// store re-places it, then the editor saves any text edits and closes, the
+// way the backdrop does.
+async function onMoved(rule: Rule) {
+  store.placeMovedRule(rule);
+  await save();
+}
+
 async function remove() {
   if (props.ruleId === null) return;
   if (!confirm("Delete this rule? This cannot be undone.")) return;
@@ -210,6 +220,14 @@ watch(() => props.ruleId, load);
         </p>
       </fieldset>
 
+      <RuleHomePicker
+        v-if="!isCreating && ruleId !== null && store.currentRule"
+        :rule-id="ruleId"
+        :topic-id="store.currentRule.topic_id"
+        :project-id="store.currentRule.project_id"
+        @moved="onMoved"
+      />
+
       <section v-if="relations.length" class="relations">
         <h3>Related rules</h3>
         <ul>