Fix `viewer.html` not rendered when first log in `results.yaml`

Summary

• Fix viewer.html not being rendered as an iframe when it is the first log entry in TMT results.yaml
• Add tmt-html-artifact-first test scenario to cover this case

Root cause

When viewer.html is the first log entry in results.yaml, TMT maps it to name="testout.log" in results.xml. Oculus only checked the name attribute for .html extension, so it missed this case and rendered the HTML as plain text via log-viewer instead of as an iframe.

Broken (name="testout.log", href="...viewer.html"):

<log href="...viewer.html" name="testout.log" />

Working (name="data/viewer.html", href="...viewer.html"):

<log href="...viewer.html" name="data/viewer.html" />

Fix

Also check the href attribute for .html extension in selectInlineTestcaseLogs().

Reproducer

• Broken (before fix): https://artifacts.dev.testing-farm.io/aa30da3c-ba3d-403b-b2d5-6d495e914956/
• Working (viewer.html not first): https://artifacts.dev.testing-farm.io/43b3339e-8e95-4e84-b785-83d37225b1d2/

Screenshot (after fix)

Assisted-by: Claude Code