Add alt Attributes for Company Logos and Media Gallery Images

### Is your feature request related to a problem? Please describe
Currently, when users submit job listings via the front-end submission form, images such as company logos and media gallery uploads do not have `alt` attributes set automatically. This is an accessibility and SEO concern, as screen readers cannot interpret these images, and search engines may not index them properly.

### Describe the solution you'd like
For company logos and gallery images, allow users to optionally specify alt text during submission.

### Describe alternatives you've considered
Automatically generate `alt` attributes for images uploaded through the job submission form.

### Additional context

No files or tests are named. Start by locating the front-end job submission handling for company logos and media gallery uploads, then trace how uploaded images are rendered; done means submitters can optionally provide alt text and the resulting images expose it correctly, with an appropriate test added or updated.

Written by the indexing model from the issue text.