feat(db): add migration chain CI validation, pre-commit hook, script template, docs, and tests

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

migrations/script.py.mako

@@ -0,0 +1,40 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+
+from typing import Union
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, None] = ${repr(down_revision)}
+depends_on: Union[str, None] = None
+
+
+def upgrade() -> None:
+    """${message}."""
+    # Use ``op.batch_alter_table()`` for SQLite compatibility.
+    # Always check whether the table/column already exists before altering
+    # to keep migrations idempotent (safe to re-run).
+    #
+    # Example – add a column only if it is missing:
+    #
+    #     conn = op.get_bind()
+    #     inspector = sa.inspect(conn)
+    #     if "my_table" in inspector.get_table_names():
+    #         existing = {c["name"] for c in inspector.get_columns("my_table")}
+    #         if "new_col" not in existing:
+    #             with op.batch_alter_table("my_table") as batch_op:
+    #                 batch_op.add_column(sa.Column("new_col", sa.String(128), nullable=True))
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    """Reverse ${message}."""
+    ${downgrades if downgrades else "pass"}