Remove testBuildType mechanism from UI test modules (#5388)

* fix(build): Remove testBuildType mechanism from UI test modules

The debug and release build types were configured identically in
both uitest modules (same minification, proguard rules, signing).
Disable the debug variant unconditionally, hardcode testBuildType
to release, and combine the now-simplified Gradle invocations.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix(build): Combine Gradle invocations in AGENTS.md

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>