🐛 Fix smoke test path handling for direct function URLs

[gepser]

Problem

Deploy succeeded, but smoke tests failed when using direct Cloud Function URL output:

https://...cloudfunctions.net/progress

The smoke script appended /progress again, resulting in:

.../progress/progress/76.

Fix

In scripts/smoke.sh, changed default expansion to only apply when PROGRESS_PATH is unset (not when explicitly empty):

• from: ${PROGRESS_PATH:-/progress}
• to: ${PROGRESS_PATH-/progress}

This preserves PROGRESS_PATH="" from deploy workflow and supports both modes:

• domain root + default /progress
• direct function URL + empty path

Validation

• Local smoke with root base URL: ✅
• Local smoke with direct function URL (PROGRESS_PATH=""): ✅