feat(rules): always_on rulebook flag + Scribe-first prompt

Adds rulebooks.always_on (migration 0058) and a new list_always_on_rules
MCP tool so a session-start eager pull can fetch standing rules without
needing an active-project notion. Updates _INSTRUCTIONS so Claude calls
the new tool at session start and codifies engineering rules in Scribe
rather than CLAUDE.md / auto-memory.

Seeds FabledSword family rulebook to always_on=true on migrate, matching
its design role as the cross-project standards rulebook.

Frontend: badge in RulebookListPane for always-on rulebooks; toggle in
RulebookDetailPane header bound to a new toggleAlwaysOn store action.

This is S1+S2 of the rules-consolidation plan (Scribe task #508). S3
(project-scoped rules) and S4 (enter_project handshake) follow.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/stores/rulebooks.ts

@@ -54,13 +54,19 @@ export const useRulebooksStore = defineStore("rulebooks", () => {
     return rb;
   }
 
-  async function updateRulebook(id: number, data: Partial<Pick<Rulebook, "title" | "description">>) {
+  async function updateRulebook(id: number, data: Partial<Pick<Rulebook, "title" | "description" | "always_on">>) {
     const rb = await api.updateRulebook(id, data);
     const idx = rulebooks.value.findIndex((r) => r.id === id);
     if (idx >= 0) rulebooks.value[idx] = rb;
     return rb;
   }
 
+  async function toggleAlwaysOn(id: number) {
+    const current = rulebooks.value.find((r) => r.id === id);
+    if (!current) return;
+    return updateRulebook(id, { always_on: !current.always_on });
+  }
+
   async function deleteRulebook(id: number) {
     await api.deleteRulebook(id);
     rulebooks.value = rulebooks.value.filter((r) => r.id !== id);
@@ -121,7 +127,7 @@ export const useRulebooksStore = defineStore("rulebooks", () => {
   return {
     rulebooks, topicsByRulebook, rulesByTopic, currentRule, loading,
     fetchRulebooks, fetchTopics, fetchRules, fetchRule,
-    createRulebook, updateRulebook, deleteRulebook,
+    createRulebook, updateRulebook, toggleAlwaysOn, deleteRulebook,
     createTopic, updateTopic, deleteTopic,
     createRule, updateRule, deleteRule,
   };