Add missing edge case test for root path (/) and expand test coverage
for preview FQDN generation. Tests verify that ports and paths are
correctly preserved in preview URLs while excluding root paths.
Fixes#2184
The {{port}} template variable was undocumented and caused a double port bug
when used in preview URL templates. Since ports are always appended to the final
URL anyway, we remove {{port}} substitution entirely and ensure consistent port
handling across ApplicationPreview, PreviewsCompose, and the applicationParser helper.
Also fix PreviewsCompose.php which wasn't preserving ports at all, and improve
the Blade template formatting in previews-compose.blade.php.
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Co-Authored-By: Claude <noreply@anthropic.com>
