Fix language picker current label

[zzj3720]

Summary

• Resolve stored regional/default language identifiers to supported app localization picker options
• Bind General/Appearance language pickers to that resolved selection so the current label is visible before switching
• Add regression tests for regional and empty/default language values

Validation

• git hook: swiftformat + swiftlint passed
• manual helper check: zh-Hans-CN -> zh-Hans, en-US -> en, empty preferred zh-Hans-CN -> zh-Hans
• app build / GUI smoke pending

[JimmFly]

No blocking findings from my static review. The regional language resolution is scoped to the picker binding, keeps the stored language behavior intact, and the new unit test imports the correct OpenBridge module. Public CI checks are green; I did not run a local macOS build from this broker session.

[cuesurfbot]

独立静态 review。

• 新的 macos/OpenBridgeUnitTests/Suites/AppLanguageSelectionTests.swift 使用 @testable import OpenBridge，与同目录其他测试一致；该 repo 单一 macos/OpenBridge.xcodeproj，module 名即 OpenBridge，没有 cueboard 那种 Bridge / Cueboard 名字漂移。
• AppLanguageSelection 与 cueboard PR #2056 的实现完全等价；regional / empty / unsupported / available filter 四条单元测试足以覆盖核心 resolve 逻辑。
• AppearanceSettingsView / GeneralSettingsView 中 languageSelection binding 的 getter 把 stored value 解析到 Picker 选项，setter 直接写回 settingsManager.language，仅在用户主动选择时触发，原 Locale.preferredLanguages.first 默认值（regional）行为不会被悄悄重写。
• Public CI（Web / Sandbox VM Go Tests / Repository Hygiene）全部绿色。

执行情况：未在本地跑 macOS build；该 repo 不在 Public CI 中跑 macOS。没有 blocking issue。