Fix German Strap gender in Android onboarding

[ben-tsk]

What this PR does

Follows up on ryanbr#1029 by using masculine grammatical forms for Strap consistently in the German Android onboarding copy.

• Corrects nine accusative forms from dein Strap to deinen Strap
• Corrects the corresponding pronoun from es to ihn

Type of change

• Bug fix
• New feature
• Refactor / cleanup
• Documentation
• CI / tooling

How it was tested

• ./gradlew assembleFullDebug
• ./gradlew testFullDebugUnitTest
• Repository i18n regression audit against the current main
• Repository source-hygiene check
• XML parse validation for android/app/src/main/res/values-de/strings.xml
• git diff --check
• Verified all nine affected resources against the current main

The Android build, unit tests, i18n audit, and source-hygiene check all passed in GitHub Actions.

Checklist

• Swift package tests pass for any package I touched (swift test in Packages/<name>) — not applicable; no Swift package was touched
• Android unit tests pass if I touched android/ (./gradlew testFullDebugUnitTest)
• No new build warnings introduced
• UI changes use only StrandDesign tokens — no hardcoded colors, fonts, or spacing
• No hardcoded hex frame bytes; protocol facts live in the schema / decoders
• Follows the conventions in docs/CONTRIBUTING.md
• I did not commit generated output (Strand.xcodeproj/) or any secrets/keystores

Related issues

Follow-up to ryanbr#1029.

[ben-tsk]

Validation completed successfully. Superseded by upstream PR ryanbr#1358.