ci(workflow): inject keystore signing properties into apk build (AI-generated)

[GiZano]

This pull request description was written by an AI agent.

Description

Updates the Android APK build workflow (build-apk.yml) to sign release builds using Gradle injected properties:

• Decodes the KEYSTORE_BASE64 secret into release.keystore in the project root prior to building.
• Injects Android signing parameters (-Pandroid.injected.signing.store.file, -Pandroid.injected.signing.store.password, -Pandroid.injected.signing.key.alias, -Pandroid.injected.signing.key.password) into ./gradlew assembleRelease using environment variables populated from GitHub Secrets.

Testing Instructions

1. Verify workflow syntax and formatting (npx prettier --check .github/workflows/build-apk.yml).
2. Verify release.keystore generation and Gradle signing resolution in CI runs.

Checklist

• My code follows the guidelines in CONTRIBUTING.md.
• I have run npm run lint and npx tsc --noEmit and there are no errors.
• My changes do not introduce unnecessary complex UI libraries.

AI Generation Disclosure

• Was AI used to generate code in this PR? Yes
• If Yes, which tool/model? Antigravity (Google DeepMind) / Gemini 3.8 Flash
• Files or line ranges generated by AI:
  • .github/workflows/build-apk.yml (lines 40-56)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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