build: reproducible APK build pipeline

[JP1Q]

Branch

build/apk-pipeline-buildozer

Priority

Medium

Timeline

Week 6

Goal

Make APK build repeatable for contributors.

Scope

• Clean up Buildozer config
• Document required environment/dependencies
• Produce debug APK artifact
• Add troubleshooting notes

Acceptance Criteria

• Fresh environment can build APK via docs
• Dependency versions are documented
• Common failures have known fixes