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>

alembic/versions/0058_rulebook_always_on.py

@@ -0,0 +1,39 @@
+"""rulebook always_on flag
+
+Revision ID: 0058
+Revises: 0057
+Create Date: 2026-06-01
+
+Adds a boolean `always_on` to the `rulebooks` table. Rules from rulebooks
+flagged always_on are loaded at session start by the new
+`list_always_on_rules` MCP tool — they apply regardless of which project
+(if any) is in scope. Seeds the FabledSword family rulebook to always_on
+because that's the cross-project standards rulebook by design.
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = "0058"
+down_revision = "0057"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "rulebooks",
+        sa.Column(
+            "always_on",
+            sa.Boolean(),
+            nullable=False,
+            server_default=sa.text("false"),
+        ),
+    )
+    op.execute(
+        "UPDATE rulebooks SET always_on = TRUE WHERE title = 'FabledSword family'"
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("rulebooks", "always_on")