fix: Replace automation stubs with real execution engine

- Replace automation execute stub with run_automation() from execution_engine.py
- Replace agent execute stub with run_agent() from agent_runner.py
- Persist automation settings in system_settings.automation_config JSONB
- Add migration 0034 for automation_config column
- Settings are now saved and loaded from database instead of being ignored

alembic/versions/0034_automation_config.py

@@ -0,0 +1,27 @@
+"""Add automation_config JSONB column to system_settings.
+
+Revision ID: 0034
+Revises: 0033_bank_accounts
+Create Date: 2026-07-25
+"""
+
+from __future__ import annotations
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import JSONB
+
+revision: str = "0034_automation_config"
+down_revision: Union[str, None] = "0033_bank_accounts"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column("system_settings", sa.Column("automation_config", JSONB, nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column("system_settings", "automation_config")