3. Add core playground types and utilities

[anish-sahoo]

• shared playground types, theme config, test setup, and openapi/terminal utilities
• includes colocated utility unit tests
• cog-playground stack: 1. Add Go playground server and handlers #3109, 2. Add playground frontend scaffold and early CI #3108, 3. Add core playground types and utilities #3114, 4. Add shared playground UI and JSON editor #3110/5. Add Cog playground API client #3106, 6. Add playground connection feature #3105/7. Add playground input controls and validation #3111/8. Add playground prediction controls and output #3107, 9. Wire up Cog playground and documentation #3113, 10. Compose playground app and add browser e2e #3112

[ask-bonk]

I'm Bonk, and I've done a quick review of your PR.

This PR adds core shared types (health, JSON, OpenAPI, prediction) and utility functions (theme, OpenAPI resolution, terminal rendering) with colocated tests for the new playground feature.

I didn't find any actionable issues. The code is well-typed, thoroughly tested, and follows good practices.

LGTM

github run