Improve German Breathe localization

[ben-tsk]

What this PR does

Improves the German localization of the Breathe experience on Android, iOS, and macOS.

• Rewrites 15 overly literal or grammatically inconsistent German strings
• Uses informal du consistently
• Clarifies the user-facing descriptions of breathing pace, R-R intervals, RMSSD, and haptic guidance
• Keeps the Android resources and Apple String Catalog aligned

Type of change

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

How it was tested

• Android debug APK build (./gradlew assembleFullDebug)
• Android unit tests (./gradlew testFullDebugUnitTest)
• macOS Strand build and tests
• iOS simulator build
• Repository i18n regression audit against the current main
• Source Hygiene workflow
• XML parse validation for android/app/src/main/res/values-de/strings.xml
• JSON parse validation for Strand/Resources/Localizable.xcstrings
• git diff --check
• Reviewed all 33 German Breathe strings against the English source copy and their UI context

All GitHub Actions checks passed in the fork: https://github.com/ben-tsk/noop/pull/3/checks

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 — warnings emitted by the Apple jobs are pre-existing and unrelated to the two localization resource files changed here
• 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

None.