feat(automation): add Zapier and Make.com integration

Add REST hooks subscription endpoints, incoming action endpoints, and
Zapier-compatible flat payload format for automation platform integration.

- AutomationHook model for webhook subscriptions
- POST /api/automation/hooks/subscribe and DELETE /hooks/{id}
- GET /api/automation/triggers/sample/{event} for Zapier field mapping
- POST /api/automation/actions/upload for incoming document uploads
- Celery task with retry for async hook delivery
- Integration with existing webhook dispatch flow
- 30 passing tests covering all new functionality

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

migrations/versions/027_add_automation_hooks.py

@@ -0,0 +1,39 @@
+"""Add automation_hooks table for Zapier / Make.com webhook subscriptions.
+
+Revision ID: 027_add_automation_hooks
+Revises: 026_add_scheduled_jobs
+Create Date: 2026-03-09
+"""
+
+from typing import Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "027_add_automation_hooks"
+down_revision: Union[str, None] = "026_add_scheduled_jobs"
+depends_on: Union[str, None] = None
+
+
+def upgrade() -> None:
+    """Create automation_hooks table."""
+    op.create_table(
+        "automation_hooks",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("target_url", sa.String(), nullable=False),
+        sa.Column("secret", sa.String(), nullable=True),
+        sa.Column("events", sa.Text(), nullable=False),
+        sa.Column("is_active", sa.Boolean(), nullable=False, server_default="1"),
+        sa.Column("hook_type", sa.String(50), nullable=False, server_default="generic"),
+        sa.Column("description", sa.String(), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now()),
+        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.func.now()),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index("ix_automation_hooks_id", "automation_hooks", ["id"])
+
+
+def downgrade() -> None:
+    """Drop automation_hooks table."""
+    op.drop_index("ix_automation_hooks_id", "automation_hooks")
+    op.drop_table("automation_hooks")