[2.x] [Tags] Drop legacy unused background columns from tags table

[Abdooo2235]

Summary

This PR removes two legacy columns from the tags table that are no longer used by current tags flows:

• background_path
• background_mode

Fixes #4527.

What changed

• Added migration using Migration::dropColumns() to remove both legacy columns.
• Removed backgroundUrl and backgroundMode from the tags API resource.
• Removed stale background accessors from the frontend Tag model.
• Removed stale references from the tag factory and model docblocks.
• Added an integration schema test asserting those columns are absent after migrations.

Backward compatibility

• This is an intentional clean break for 2.x pre-stable, aligned with review feedback.
• Existing data in removed columns is dropped as part of schema cleanup.

Scope note

An unrelated local change in extensions/tags/js/tsconfig.json was intentionally excluded from this PR to keep the fix focused.

Testing

• Added: extensions/tags/tests/integration/api/tags/SchemaTest.php
• Local test execution in this environment is blocked because phpunit is not available (sh: 1: phpunit: not found).

[DavideIadeluca]

Thanks for picking up the issue I opened. Have you considered using Flarum’s migration helper? The migration in the PR feels a bit more complex than necessary and could likely be simplified along these lines:

use Flarum\Database\Migration;

return Migration::dropColumns('tags', [
    'background_path' => [..],
    'background_mode' => [..],
]);

Note that with Migration::dropColumns() you still need to specify the column constraints and metadata, similar to what you would define in the up migration.

Another thing that stood out in the PR is that the attributes are still present. If background_mode and background_path are no longer required, wouldn’t this effectively become dead code? It might be better to remove them entirely and go for a clean break.

Since Flarum 2 hasn’t been tagged as stable yet, a breaking change like this should still be acceptable without creating backwards compatibility concerns.

[Abdooo2235]

@DavideIadeluca thanks a lot for the thoughtful review and for opening this issue in the first place.

Great call on both points. I updated the PR accordingly:

• Switched the migration to use Migration::dropColumns() with full column definitions.
• Removed the leftover backgroundUrl / backgroundMode attributes from the API resource.
• Removed the corresponding stale accessors from the frontend Tag model so there’s no dead code path left.

I agree with your reasoning about 2.x still being pre-stable, so I went with the clean break approach here.

I also reran the tags integration suite after the update:
composer test:integration → OK (127 tests, 213 assertions).

Really appreciate the guidance.