fix: correct the request URL construction in playground

[jianzs]

Previously, the playground was building request URLs by removing the playground suffix and appending stream_log. This worked when the URL ended with playground, but failed for URLs ending with index.html. The issue was the code only checked for URLs ending with playground and did not account for index.html endings.

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[eyurtsev]

@jianzs thank you, I'll review and release next week

[jianzs]

@eyurtsev Hi there! I was wondering if you might have some time to review the PR I submitted? Please feel free to point out any issues or concerns at your convenience.