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>

tests/test_mcp_tool_rulebooks.py

@@ -179,8 +179,59 @@ def test_register_attaches_all_sixteen_tools():
             return decorator
 
     register(FakeMCP())
-    assert len(registered) == 16
+    assert len(registered) == 17
     # spot-check a few names
     assert "list_rulebooks" in registered
     assert "create_rule" in registered
     assert "subscribe_project_to_rulebook" in registered
+    assert "list_always_on_rules" in registered
+
+
+@pytest.mark.asyncio
+async def test_list_always_on_rules_returns_empty_when_no_always_on_rulebooks():
+    with patch(
+        "fabledassistant.mcp.tools.rulebooks.rulebooks_svc.list_always_on_rules",
+        AsyncMock(return_value=[]),
+    ):
+        from fabledassistant.mcp.tools.rulebooks import list_always_on_rules
+        out = await list_always_on_rules()
+    assert out == {"rules": [], "total": 0}
+
+
+@pytest.mark.asyncio
+async def test_list_always_on_rules_projects_each_rule():
+    rules = [_fake_rule(id=100), _fake_rule(id=101)]
+    with patch(
+        "fabledassistant.mcp.tools.rulebooks.rulebooks_svc.list_always_on_rules",
+        AsyncMock(return_value=rules),
+    ):
+        from fabledassistant.mcp.tools.rulebooks import list_always_on_rules
+        out = await list_always_on_rules()
+    assert out["total"] == 2
+    assert {r["id"] for r in out["rules"]} == {100, 101}
+    assert all("topic_id" in r for r in out["rules"])
+
+
+@pytest.mark.asyncio
+async def test_update_rulebook_forwards_always_on_when_set():
+    rb = _fake_rulebook(id=1, title="t")
+    mock = AsyncMock(return_value=rb)
+    with patch("fabledassistant.mcp.tools.rulebooks.rulebooks_svc.update_rulebook", mock):
+        from fabledassistant.mcp.tools.rulebooks import update_rulebook
+        await update_rulebook(rulebook_id=1, always_on=True)
+    kwargs = mock.call_args.kwargs
+    assert kwargs.get("always_on") is True
+    assert "title" not in kwargs
+    assert "description" not in kwargs
+
+
+@pytest.mark.asyncio
+async def test_update_rulebook_omits_always_on_when_none():
+    rb = _fake_rulebook(id=1, title="t")
+    mock = AsyncMock(return_value=rb)
+    with patch("fabledassistant.mcp.tools.rulebooks.rulebooks_svc.update_rulebook", mock):
+        from fabledassistant.mcp.tools.rulebooks import update_rulebook
+        await update_rulebook(rulebook_id=1, title="new title")
+    kwargs = mock.call_args.kwargs
+    assert "always_on" not in kwargs
+    assert kwargs["title"] == "new title"