feat: add Vercel and Codex themes

[CHENG-LIANG1]

Summary

• add a Vercel theme with distinct light and dark variants based on the official Geist color system
• add a dark-first Codex theme based on the official Codex TUI styling conventions, while retaining light-mode compatibility
• register both themes in the others collection and add translations for all five supported locales
• include renderer-generated previews for the gallery

Design sources

• Vercel palette: vercel/next.js DevTools color tokens
• Codex semantics: openai/codex TUI style guide and background/accent implementation

Validation

• pnpm build
• pnpm exec tsc --noEmit
• targeted Prettier check for all changed TypeScript and locale files
• jq empty messages/*.json
• browser-rendered visual review of Vercel light/dark and Codex dark previews

Note

The repository-wide pnpm format:check still reports three pre-existing formatting issues in lib/themes/others/peppa.ts, lib/themes/others/pulse-interactive.ts, and SKILL/SKILL.md; none are touched by this PR.

[vercel]

@CHENG-LIANG1 is attempting to deploy a commit to the Okapippo Team on Vercel.

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