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>

src/fabledassistant/services/rulebooks.py

@@ -72,7 +72,7 @@ async def update_rulebook(
         rb = result.scalar_one_or_none()
         if rb is None:
             return None
-        allowed = {"title", "description"}
+        allowed = {"title", "description", "always_on"}
         for key, value in fields.items():
             if key in allowed and value is not None:
                 setattr(rb, key, value)
@@ -305,6 +305,33 @@ async def list_rules(
         return list(result.scalars().all())
 
 
+async def list_always_on_rules(user_id: int, limit: int = 100) -> list[Rule]:
+    """Return all rules from rulebooks flagged always_on for the user.
+
+    Called by the MCP tool of the same name at session start to load the
+    standing rules that apply regardless of which project (if any) is in
+    scope. Ordering matches list_rules so results are stable across calls.
+    """
+    async with async_session() as session:
+        result = await session.execute(
+            select(Rule)
+            .join(RulebookTopic, Rule.topic_id == RulebookTopic.id)
+            .join(Rulebook, RulebookTopic.rulebook_id == Rulebook.id)
+            .where(
+                Rulebook.owner_user_id == user_id,
+                Rulebook.always_on.is_(True),
+                Rule.deleted_at.is_(None),
+                RulebookTopic.deleted_at.is_(None),
+                Rulebook.deleted_at.is_(None),
+            )
+            .order_by(
+                Rulebook.id, RulebookTopic.order_index, Rule.order_index, Rule.title,
+            )
+            .limit(limit)
+        )
+        return list(result.scalars().all())
+
+
 async def get_rule(rule_id: int, user_id: int) -> Optional[Rule]:
     async with async_session() as session:
         result = await session.execute(