feat: migrate from playground

[astykyj]

Summary

• Replace the public repository tree with the current Stave provider runtime upgrade branch contents.
• Preserve sendbird/stave main history by using a bridge commit on top of the existing main branch, since direct force-push is blocked by repository rules.
• Includes Claude Agent SDK and Codex SDK upgrades, GPT-5.5 Codex default, and deprecated Codex on-failure approval policy removal from UI/runtime options.

Verification

• bun run typecheck
• bun test tests/model-catalog.test.ts tests/stave-auto-profile.test.ts tests/stave-router.test.ts tests/provider-runtime-options.test.ts tests/codex-sdk-runtime.test.ts tests/codex-app-server-runtime.test.ts