Fix: Cast LazyString to str before DB commit

[jilkka]

Added force_string validator to ensure label is string before DB commit.

Summary

Fixed a 500 Internal Server Error occurring when adding vehicle specifications during new vehicle creation and adding to existing vehicle.
LazyStrings were being passed directly to SQLite resulting in crash.

Changelog

• Added: A @validates decorator in models.py to automatically cast specification labels to standard strings before they reach the database.

• Fixed: sqlalchemy.exc.ProgrammingError when saving predefined vehicle spec types during new vehicle creation and after.

Testing

How were these changes tested?

• Tested locally
• Tested with Docker image

[lyonsden69]

I can confirm this is still happening on v0.15.0 using the Docker image on a Synology NAS.

What I found:

• Adding preset vehicle specs causes a 500 error
• Adding custom specs works normally
• The entered value does not seem to matter

Relevant log output:
sqlalchemy.exc.ProgrammingError: (sqlite3.ProgrammingError) Error binding parameter 3: type 'LazyString' is not supported
[SQL: INSERT INTO vehicle_specs (vehicle_id, spec_type, label, value, created_at) VALUES (?, ?, ?, ?, ?) RETURNING id]
[parameters: (1, 'tire_size_front', l'Front Tire Size', '225/65/R17', '2026-03-13 16:25:15.342948')]

Thanks for the fix in PR #97 — happy to test once it makes it into a release.