Add language setting with full Vietnamese localization

[datlechin]

Summary

• Add language setting in Settings > General with three options: System, English, Vietnamese
• Add Xcode String Catalog (Localizable.xcstrings) with 637 localized strings — 100% Vietnamese coverage
• Migrate hardcoded English strings to String(localized:) across 48 files
• Show restart notice only when language is changed during the current session
• Fix query timeout picker to gracefully handle non-standard stored values

Changes

Area	Files	Description
Language setting	AppSettings.swift, GeneralSettingsView.swift, AppSettingsManager.swift	AppLanguage enum, picker UI, apply on startup/change
String Catalog	Localizable.xcstrings, project.pbxproj	637 strings, vi added to knownRegions
Localization migration	48 view/model files	String(localized:) for all user-facing strings
Picker fix	GeneralSettingsView.swift	Include non-standard stored timeout value in picker tags
Docs	CHANGELOG.md, TRACKING.md	Updated localization status and changelog

Test plan

• Settings > General shows Language picker with 3 options (System, English, Tiếng Việt)
• Selecting "Tiếng Việt" → restart → UI displays Vietnamese
• Selecting "System" → restart → falls back to macOS system language
• Restart notice appears only when language is changed, not on fresh open
• No "invalid tag" picker warnings in console
• Build succeeds with zero errors