refactor: standardize conjugate label language checks using ScribeLan…

[akkicodes-dev]

Summary

Standardizes conjugate label mode switching logic to use the ScribeLanguage enum instead of raw string comparisons, following the same pattern established in #672 and #673.

Changes

• KeyboardUIManager.kt: Replaced hardcoded string checks (language == "English", language in listOf("Russian", "Swedish")) with ScribeLanguage.fromDisplayName() enum comparisons for conjugate grid layout selection (2x2/3x2)
• ConjugateViewModel.kt: Replaced duplicated hardcoded language alias list (listOf("EN", "FR", "DE", "IT", "PT", "RU", "ES", "SV"), used in 2 places) with ScribeLanguage.entries.map { it.isoCode } as a single source of truth

Testing

• ./gradlew lintKotlin detekt — passed
• Added 6 new unit tests in KeyboardUIManagerTest.kt covering grid layout selection for English/Russian/Swedish/German, sub-selection priority, and unknown-language fallback
• Added 3 new unit tests in ConjugateViewModelTest.kt verifying the enum-derived alias list matches the previous hardcoded list exactly
• ./gradlew testKeyboardsDebugUnitTest testConjugateDebugUnitTest — all tests pass (BUILD SUCCESSFUL)
• Note: physical device testing wasn't available for this PR, so verification relies on comprehensive unit test coverage of the changed logic instead

Note

Parts of this PR were AI-assisted (Antigravity); all changes were manually reviewed line-by-line, verified via local build/lint/test, and cross-checked against the codebase before submission.

Part of #426. Follows the pattern from #672 / #673.

[Roniscend]

The language list code is repeated in two places and could be combined into one, and it'd be good to add a test for what happens if an unrecognized language is passed in.

[akkicodes-dev]

Thanks for the feedback @Roniscend! I've made both changes:

1. Extracted the duplicated ScribeLanguage.entries.map { it.isoCode } into a single SUPPORTED_ALIASES constant in a companion object — both getDownloadedLanguages() and performSearch() now reference it.
2. Added edge-case tests for unrecognized language handling in ConjugateViewModelTest.kt (unrecognized DB files, format edge cases, and deserialization of unrecognized aliases). The KeyboardUIManagerTest.kt already had updateUI_UnknownLanguageString_FallsBackSafelyWithoutCrashing covering the UI-layer case.

All lint/detekt checks and unit tests pass. Let me know if this looks good!