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.

OSGKeyboardExt/Utilities/KeyboardSoundFeedback.swift

@@ -0,0 +1,41 @@
+// KeyboardSoundFeedback.swift
+// OSGKeyboard · Keyboard Extension
+//
+// Plays the built-in iOS keyboard click sounds so the custom bottom-row
+// keys (space / return / delete) sound identical to the stock keyboard.
+
+import UIKit
+import AudioToolbox
+
+/// 让键盘扩展支持系统点击音。`UIDevice.playInputClick()` 只有在「某个
+/// 可见的输入视图遵循本协议且返回 true」时才会发声。键盘扩展的根视图
+/// 由系统包在一个 `UIInputView` 里，因此对它做追溯遵循即可开启点击音。
+extension UIInputView: @retroactive UIInputViewAudioFeedback {
+    public var enableInputClicksWhenVisible: Bool { true }
+}
+
+/// 播放系统键盘原声，让空格 / 回车 / 删除键与系统键盘完全一致。
+///
+/// 空格 / 回车走官方 `playInputClick()`：这是键盘扩展里最可靠的方式，
+/// 会自动尊重「键盘咔嗒声」设置与响铃/静音开关。删除键因为 `playInputClick()`
+/// 无法选择其专属音色，改用系统删除音 `1155`。两者都要求扩展已开启
+/// 「完全访问」才会发声。
+enum KeyboardSoundFeedback {
+    /// 删除键音（单次删除，以及长按连删时的每一次删除）。
+    private static let deleteSoundID: SystemSoundID = 1155
+
+    /// 普通按键点击音（空格、回车）。
+    @MainActor
+    static func keyClick() {
+        UIDevice.current.playInputClick()
+    }
+
+    /// 删除键点击音。
+    static func deleteClick() {
+        // 未开「完全访问」时该调用是无效空操作，但仍可能短暂阻塞，
+        // 放到后台线程可保证连删手感不卡顿。
+        DispatchQueue.global(qos: .userInteractive).async {
+            AudioServicesPlaySystemSound(deleteSoundID)
+        }
+    }
+}