Fix related candidate default selection

[limeimetw]

Summary

• restore the pre-limeendkey default candidate selection rules for the visible candidate strip
• keep related/association-only candidates unhighlighted so Enter/Search/Return can pass through after composition ends
• split explicit %limeendkey resolution from normal/default candidate selection so 中文鍵盤,.按鍵問題 #96 behavior stays independent
• add regression coverage for legacy default selection, related-only no-default selection, and Chinese-punctuation end-key resolution

Validation

• ANDROID_HOME=$HOME/Android/Sdk ANDROID_SDK_ROOT=$HOME/Android/Sdk ./gradlew :app:compileDebugJavaWithJavac :app:compileDebugAndroidTestJavaWithJavac
• git diff --check

Connected instrumentation was attempted for the new #104 regression test but WSL has no connected Android device/emulator (No connected devices!).

Fixes #104