feat: AppSetting model and migration 0004

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fablednetmon/migrations/versions/0004_app_settings.py

@@ -0,0 +1,27 @@
+"""App settings table
+
+Revision ID: 0004_app_settings
+Revises: 0003_ansible_runs
+Create Date: 2026-03-18
+"""
+from typing import Sequence, Union
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = "0004_app_settings"
+down_revision: Union[str, None] = "0003_ansible_runs"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "app_settings",
+        sa.Column("key", sa.String(128), primary_key=True),
+        sa.Column("value_json", sa.Text, nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("app_settings")