feat(db): add database version tracking and automated upgrades

[Ludy87]

Description of Changes

• Introduce database version tracking entity and repository to persist the last applied schema/data version.
• Add a migration framework with a MigrationStep interface and implement an H2-specific, data-only migration from 0.33.1 to 0.34.0 that imports user-facing data from the latest backup without altering the new schema.
• Refactor DatabaseService to implement a new DatabaseServiceInterface; expose utility methods for linked tables, identity handling, and backup imports; and add migrateDatabase() orchestration.
• Call databaseService.migrateDatabase() during initial security setup to run migrations early on startup.
• Swap controller dependencies from DatabaseService to DatabaseServiceInterface; update signatures to surface SQLException/UnsupportedProviderException where appropriate.
• Simplify H2SQLCondition: enable H2-specific beans when no custom datasource is configured (instead of checking system.datasource.type).
• Minor robustness tweak: use constant-first equals for team name comparison in internal API user reassignment.

Why the change was made

• Provide a safe, idempotent path to carry user data from older H2 backups into the new schema without DDL changes, improving upgrade reliability.
• Persist an application-level database version to avoid re-running data migrations and to make future steps explicit.
• Decouple controllers from a concrete service and centralize migration/backup utilities to make the codebase easier to test and maintain.
• Ensure migrations run automatically on boot for H2 setups, reducing operational friction.

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Checklist

General

• [x] I have read the Contribution Guidelines
• [x] I have read the Stirling-PDF Developer Guide (if applicable)
• [ ] I have read the How to add new languages to Stirling-PDF (if applicable)
• [ ] I have performed a self-review of my own code
• [ ] My changes generate no new warnings

Documentation

• [ ] I have updated relevant docs on Stirling-PDF's doc repo (if functionality has heavily changed)
• [ ] I have read the section Add New Translation Tags (for new translation tags only)

UI Changes (if applicable)

• [ ] Screenshots or videos demonstrating the UI changes are attached (e.g., as comments or direct attachments in the PR)

Testing (if applicable)

• [ ] I have tested my changes locally. Refer to the Testing Guide for more details.

[Frooodle]

For database tracking and migration might be good to use spring flyway

[Ludy87]

For database tracking and migration might be good to use spring flyway

I basically went the same route, just without the additional library. Because with Flyway, a migration*.sql file would also have to be applied. Now, only four files have been added.