feat: simplified/traditional chinese preference for transcription

[mvanhorn]

Summary

• add a Simplified/Traditional Chinese preference picker in Settings → Cleanup
• post-process every transcription via CFStringTransform (ICU, no new dep) before cleanup runs
• default auto is a no-op, so existing installs are unchanged

Why this fixes #68

Whisper's multilingual model emits Traditional Chinese characters even when the user is dictating Simplified. The cleanup-prompt instructions you tried did not help because the LLM cleanup runs on top of an already-Traditional transcript and won't reliably rewrite every character. The reproducer in the issue was:

What I said: 你到底有沒有在聽我講
What appeared: 你到底有沒有在聽我講 (Traditional)
Expected: 你到底有没有在听我讲 (Simplified)

The fix runs the converter as a post-processing pass after Whisper returns and BEFORE the LLM cleanup pipeline starts, so cleanup sees the user's preferred script. Apple's CFStringTransform("Traditional-Simplified") ships the full ICU mapping table, so this is one line of conversion code rather than a hand-built character map.

Changes

• New GhostPepper/Cleanup/ChineseScriptConverter.swift:
  • enum ChineseScriptPreference { case auto, simplified, traditional } — default is auto, which is a no-op.
  • ChineseScriptConverter.convert(_:to:) wraps CFStringTransform with the right identifier per direction. Returns the input unchanged on transform failure.
• GhostPepper/AppState.swift:
  • @AppStorage("chineseScriptPreference") var chineseScriptPreferenceRaw plus a typed accessor chineseScriptPreference: ChineseScriptPreference.
  • In cleanedTranscriptionResult(_:windowContext:), text = ChineseScriptConverter.convert(text, to: chineseScriptPreference) after the override guard, before the cleanupEnabled early return. So conversion happens whether or not LLM cleanup runs.
• GhostPepper/UI/SettingsWindow.swift: a new SettingsCard("Chinese script") Picker inside cleanupSection, binding appState.chineseScriptPreference to the three enum cases.
• GhostPepper.xcodeproj/project.pbxproj: registers the two new files (project uses XcodeGen, but I made the pbxproj edits directly so consumers without xcodegen can build immediately).

Test plan

• New GhostPepperTests/ChineseScriptConverterTests.swift with five cases:

  • auto is a no-op
  • the issue's exact Traditional input converts to the issue's expected Simplified output
  • reverse direction round-trips
  • non-Chinese text is unchanged in both directions
  • empty string round-trips

• xcodebuild -project GhostPepper.xcodeproj -scheme GhostPepper -derivedDataPath build/test-derived -skipMacroValidation CODE_SIGNING_ALLOWED=NO -only-testing:GhostPepperTests/ChineseScriptConverterTests test → ** TEST SUCCEEDED **

• xcodebuild ... build → ** BUILD SUCCEEDED **

(There are 5 pre-existing failing tests on main related to testAppStateArchives* and testFluidAudioRecordingUsesSpeakerFilteringSession — unrelated to this change; they reproduce on upstream/main without this diff.)

Closes #68