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.

OSGKeyboardShared/Services/PreconfiguredKeys.local.swift.example

@@ -0,0 +1,14 @@
+// PreconfiguredKeys.local.swift.example
+// Copy to PreconfiguredKeys.local.swift (gitignored) before building.
+// `./Scripts/generate-xcodeproj.sh` creates PreconfiguredKeys.local.swift
+// from this file automatically when it is missing.
+//
+// The DeepSeek key is used ONLY by the local engine's built-in polish step.
+// Do not commit the real key — keep it in PreconfiguredKeys.local.swift on
+// your machine only.
+
+import Foundation
+
+enum PreconfiguredKeysLocal {
+    static let deepseek = "TODO_FILL_LATER_DEEPSEEK_KEY"
+}