feat(backend): add migration tracking and schema version validation

[deepsikha-dash]

Description

Implemented Alembic-style migration tracking by introducing a schema migration history table and running only pending migrations during database initialization. Added validation to detect databases created with newer, unsupported migration versions and fail startup with a clear error message. Added unit tests covering migration idempotency, migration recording, and unsupported schema version detection while ensuring existing migration behavior remains unchanged.

Related Issues

Closes #213

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

Executed the following test suites:

• pytest testing/backend/unit/test_saved_views.py -v
• pytest testing/backend/unit/test_database_connection.py -v
• pytest testing/backend/unit/test_database_workflow_versions.py -v

Verified:

• Pending migrations are applied only once.
• Applied migrations are recorded.
• Startup fails for unsupported/newer schema versions.
• Existing database behavior remains unchanged.

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.