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/components/rules/RulebookDetailPane.vue

@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import { ref, onMounted, watch } from "vue";
+import { ref, computed, onMounted, watch } from "vue";
 import { useRulebooksStore } from "@/stores/rulebooks";
 import { apiGet } from "@/api/client";
 import {
@@ -18,6 +18,10 @@ const store = useRulebooksStore();
 const isCreating = ref(false);
 const newTitle = ref("");
 
+const currentRulebook = computed(() =>
+  store.rulebooks.find((rb) => rb.id === props.rulebookId),
+);
+
 interface ProjectLite { id: number; title: string }
 const projects = ref<ProjectLite[]>([]);
 // Map<project_id, Set<rulebook_id>>
@@ -68,7 +72,17 @@ watch(() => props.rulebookId, () => {/* re-render of isSubscribed from existing
 
 <template>
   <section class="pane">
-    <header><h2>Topics</h2></header>
+    <header>
+      <h2>Topics</h2>
+      <label v-if="currentRulebook" class="always-on-toggle" title="When on, rules from this rulebook load at session start regardless of project context">
+        <input
+          type="checkbox"
+          :checked="currentRulebook.always_on"
+          @change="store.toggleAlwaysOn(currentRulebook.id)"
+        />
+        <span>Always on</span>
+      </label>
+    </header>
     <ul>
       <li
         v-for="t in topics"
@@ -109,7 +123,14 @@ watch(() => props.rulebookId, () => {/* re-render of isSubscribed from existing
 
 <style scoped>
 .pane { background: var(--color-surface, #18181b); padding: 1rem; overflow-y: auto; }
+header { display: flex; align-items: center; justify-content: space-between; gap: 1rem; }
 header h2 { font-family: Fraunces, serif; font-style: italic; margin: 0 0 0.5rem 0; }
+.always-on-toggle {
+  display: flex; align-items: center; gap: 0.4rem;
+  font-size: 0.85rem; opacity: 0.85; cursor: pointer;
+  user-select: none;
+}
+.always-on-toggle input { cursor: pointer; }
 ul { list-style: none; padding: 0; margin: 1rem 0; }
 li { padding: 0.5rem; cursor: pointer; border-radius: 6px; }
 li.active { background: var(--color-primary-bg, rgba(99,102,241,0.15)); }