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/models/rulebook.py

@@ -1,6 +1,6 @@
 from datetime import datetime, timezone
 
-from sqlalchemy import BigInteger, Column, DateTime, ForeignKey, Integer, Table, Text, UniqueConstraint
+from sqlalchemy import BigInteger, Boolean, Column, DateTime, ForeignKey, Integer, Table, Text, UniqueConstraint
 from sqlalchemy.orm import Mapped, mapped_column
 
 from fabledassistant.models import Base
@@ -16,6 +16,9 @@ class Rulebook(Base, SoftDeleteMixin):
     )
     title: Mapped[str] = mapped_column(Text)
     description: Mapped[str | None] = mapped_column(Text, nullable=True)
+    always_on: Mapped[bool] = mapped_column(
+        Boolean, default=False, nullable=False, server_default="false"
+    )
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
     )
@@ -31,6 +34,7 @@ class Rulebook(Base, SoftDeleteMixin):
             "owner_user_id": self.owner_user_id,
             "title": self.title,
             "description": self.description or "",
+            "always_on": self.always_on,
             "created_at": self.created_at.isoformat() if self.created_at else None,
             "updated_at": self.updated_at.isoformat() if self.updated_at else None,
         }