feat: SAC 0.7.4 sidebar system stats block with UI toggle

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/alembic/versions/012_ui_settings.py

@@ -0,0 +1,31 @@
+"""ui_settings singleton for SAC UI preferences
+
+Revision ID: 012
+Revises: 011
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "012"
+down_revision: Union[str, None] = "011"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "ui_settings",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("show_sidebar_system_stats", sa.Boolean(), nullable=False, server_default=sa.text("true")),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.execute(
+        "INSERT INTO ui_settings (id, show_sidebar_system_stats) VALUES (1, true)"
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("ui_settings")