Initializes Alembic with autogenerated migration covering all 11 tables
(tasks, users, projects, project_files, ontologies, graphs, simulations,
reports, system_config, invitation_tokens, password_reset_tokens).
Adds *.db to .gitignore to exclude local SQLite dev database.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Ubuntu