feat: cursor navigation, key sounds, dictionary tooling, key security

Batch of in-progress app work from the working tree.

- feat(keyboard): CursorNavigation + CursorDragPad for caret movement;
  KeyboardSoundFeedback for system key click sounds
- feat(dictionary): DictionaryAliasGenerator + PersonalDictionaryEntrySheet;
  TranscriptPostProcessor quality gate; retire DictionaryLearner
- feat(ui): TabBarVisibility handling; drop PageHeaderRow /
  PageHeaderConfirmButton; refresh views and localizable strings
- fix(security): move the hardcoded DeepSeek key out of
  PreconfiguredKeys.swift into a gitignored PreconfiguredKeys.local.swift
  (seeded from .example by generate-xcodeproj.sh)
- docs(agents): add Conventional Commits versioning + bilingual changelog rules
- chore(gitignore): ignore PreconfiguredKeys.local.swift, .cache/, pycache

Custom language model / lexicon work stays on
feature/custom-language-model-asr. Changelog bullets added under
[Unreleased]; no version bump.

OSGKeyboard/Views/EnginePickerSection.swift

@@ -102,9 +102,11 @@ struct EnginePickerSection: View {
     private func selectEngine(_ id: String) {
         withAnimation(.easeInOut(duration: 0.2)) {
             config.engineMode = id
-            // Cloud always runs ASR + LLM polish; no off/transcribe toggle.
             if id == "cloud" {
                 config.modeId = "polish"
+                if config.providerId == "deepseek" {
+                    config.apply(preset: LLMProvider.provider(id: "openai"))
+                }
             }
         }
     }