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/RulebookListPane.vue

@@ -31,6 +31,7 @@ async function submitNew() {
         @click="emit('select', rb.id)"
       >
         <span class="title">{{ rb.title }}</span>
+        <span v-if="rb.always_on" class="always-on-badge" title="Loaded at session start">always on</span>
       </li>
     </ul>
     <div class="new-rulebook">
@@ -50,9 +51,19 @@ async function submitNew() {
 .pane { background: var(--color-surface, #18181b); padding: 1rem; overflow-y: auto; }
 header h2 { font-family: Fraunces, serif; font-style: italic; margin: 0 0 0.5rem 0; }
 ul { list-style: none; padding: 0; margin: 1rem 0; }
-li { padding: 0.5rem; cursor: pointer; border-radius: 6px; }
+li { padding: 0.5rem; cursor: pointer; border-radius: 6px; display: flex; align-items: center; gap: 0.5rem; }
 li.active { background: var(--color-primary-bg, rgba(99,102,241,0.15)); }
 li:hover { background: var(--color-hover, rgba(255,255,255,0.05)); }
+.always-on-badge {
+  font-size: 0.7rem;
+  text-transform: uppercase;
+  letter-spacing: 0.05em;
+  padding: 0.1rem 0.4rem;
+  border-radius: 3px;
+  background: var(--color-accent, rgba(91,74,138,0.25));
+  color: var(--color-accent-fg, inherit);
+  margin-left: auto;
+}
 .new-rulebook { margin-top: 1rem; }
 .new-rulebook input {
   width: 100%; margin-bottom: 0.5rem;