Refine mobile CI triggers and modularize Android scripts

[shai-almog]

Summary

• tighten Android and iOS workflow triggers so native builds only run when ports, shared sources, or supporting scripts change
• move screenshot report generation and PR comment publishing logic into dedicated Python helpers used by run-android-instrumentation-tests.sh
• add documentation that describes the purpose of the scripts directory and its key entry points

Testing

• python3 -m compileall scripts/android/tests

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https://chatgpt.com/codex/tasks/task_e_68f1b0fd78a08331aa3eb616877abcda

[shai-almog]

✅ Native Android screenshot tests passed.