Manuscript.date max_length=50 causes import failure for some manuscripts

[kyrieb-ekat]

When running import_data manuscripts locally, the import fails for manuscripts
whose date field in CantusDB exceeds 50 characters. The Manuscript model
currently defines:

date = models.CharField(max_length=50, blank=True, null=True)

This silently truncates or raises a database error depending on the backend
configuration.

Steps to reproduce:

1. Follow the local setup instructions in the README
2. Run docker compose exec app python manage.py import_data manuscripts
3. Observe failure for manuscripts with long date strings

Expected behaviour: Import completes for all manuscripts, or skips
problematic records gracefully with a warning.

Suggested fix: Increase max_length to 255 (or remove the limit
entirely with TextField) and generate the corresponding migration.

[annamorphism]

isn't the date set at a 63-character maximum in CantusDB? (Frankly I'm kind of surprised there are some that are over 50 to begin with...) I guess one could set it to 255 here, but it shouldn't be possible to get a 255 character date length in the first place...