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.

OSGKeyboardTests/KeyboardOnboardingOverlayTests.swift

@@ -101,8 +101,12 @@ final class KeyboardOnboardingOverlayTests: XCTestCase {
     func testPolishIntensityRoundTrip() {
         store.setPolishIntensity(.heavy)
         XCTAssertEqual(store.polishIntensity, .heavy)
-        store.setPolishIntensity(.off)
-        XCTAssertEqual(store.polishIntensity, .off,
-                       "off should round-trip through UserDefaults (NOT skip the write)")
+        store.setPolishIntensity(.light)
+        XCTAssertEqual(store.polishIntensity, .light)
+    }
+
+    func testPolishIntensityLegacyOffMigratesToMedium() {
+        defaults.set(PolishIntensity.legacyOffRawValue, forKey: "config.polishIntensity")
+        XCTAssertEqual(store.polishIntensity, .medium)
     }
 }