test: stabilize release site interaction coverage

[zhoubot]

Summary

• give the two release-critical, multi-route interaction tests an explicit 120-second heavy-test budget
• preserve every existing assertion and browser project
• eliminate repeated Firefox failures caused by exhausting the global 30-second whole-test timeout near the final interaction

Failure evidence

Release runs 33819090989 and 33831364995 both produced the same Firefox pattern: the generic workbench test failed at 30 seconds, the TLOAD interaction test was flaky, and 95 tests passed. The deterministic site artifact passed in both runs.

Validation

• focused desktop Firefox stress: 6/6 PASS across three repetitions of both affected tests
• full cross-browser suite: 97 PASS, 8 intentional skips, 0 flaky, 0 failed
• production bilingual site build — PASS
• TypeScript typecheck — PASS
• unit tests — 14/14 PASS
• site security and Lighthouse — PASS
• site artifact validation — PASS
• make pr-check — 9/9 PASS
• make repo-check — 7/7 PASS
• git diff --check — PASS

This is test-infrastructure stabilization only; it does not change PTO ISA semantics or site content.