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/api/rulebooks.ts

@@ -5,6 +5,7 @@ export interface Rulebook {
   owner_user_id: number;
   title: string;
   description: string;
+  always_on: boolean;
   created_at: string | null;
   updated_at: string | null;
 }
@@ -65,7 +66,7 @@ export async function createRulebook(data: { title: string; description?: string
   return apiPost("/api/rulebooks", data);
 }
 
-export async function updateRulebook(id: number, data: Partial<{ title: string; description: string }>): Promise<Rulebook> {
+export async function updateRulebook(id: number, data: Partial<{ title: string; description: string; always_on: boolean }>): Promise<Rulebook> {
   return apiPatch(`/api/rulebooks/${id}`, data);
 }