[codex] Add runtime localization setting

[Maple0517]

Summary

• add a working in-app Language setting with Auto, English, and Simplified Chinese choices
• add a code-owned localization string layer shared by the app target and core-generated text
• localize the main UI, menu bar status/tooltip, insight text, local notifications, recovery/onboarding guidance, usage reports, diagnostics, support bundles, and social share text/card labels
• document the new language setting in the English and Simplified Chinese READMEs and changelog

Notes

The project already persisted AppConfig.language; this PR wires that existing preference into real UI and generated-text behavior instead of adding a parallel language system.

Server-provided/user data remains unchanged: account names, emails, URLs, model names, release names, raw server errors, numbers, and costs are not translated. Diagnostics and support bundles still report token presence only and avoid token values.

Validation

• swift build ✅
• VERSION=v0.1.11 ./scripts/build-app.sh ✅
• launched local bundle from dist/Sub2APIStatusBar.app ✅
• git diff --check ✅
• swift test ⚠️ blocked locally because the current Command Line Tools Swift environment cannot import the existing Testing module:

error: no such module 'Testing'

This also happens against the existing test target before the localization changes, so it appears to be a local toolchain issue rather than a regression in this PR.