feat: add media picker to FileUpload field

- Move MediaGridPicker from uploadcare-field to media package for sharing
- Add media picker hint action to FileUpload field (camera icon)
- Register Livewire component in MediaServiceProvider
- Update Uploadcare field to use shared MediaGridPicker
- Add tests for MediaGridPicker form component

The media picker allows users to select existing media files from a modal
grid, similar to how Uploadcare field already supports this feature.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: Baspa