docs: clarify that validation.ts helpers are test utilities, not production utilities

[shwetank-dev]

Summary

The validate* helper functions in packages/schemas/src/validation.ts (e.g. validateBundleSearchResponse, validateSkillDetail, validateBundleDetail, etc.) are named like production runtime utilities but are only used in tests (packages/schemas/tests/validation.test.ts). Production consumers handle validation differently:

Consumer	How it handles validation
Registry	Fastify serializes and validates responses via toJsonSchema()
SDK	Relies on the server-side Fastify guarantee, uses type casts
CLI	Calls schema.safeParse() directly where needed
Web	Relies on the server-side Fastify guarantee, uses type casts

Problem

A new contributor reading validation.ts would reasonably assume these helpers are meant to be wired into the SDK or web client for runtime response validation, and could waste time submitting a PR that adds them where they don't belong.

Suggested fix

Add a short doc comment at the top of validation.ts clarifying intent:

/**
 * Typed validation helpers wrapping Zod's safeParse.
 *
 * These are used in tests only. Production consumers handle validation
 * differently:
 *   - Registry: Fastify serializes and validates responses via toJsonSchema()
 *   - SDK:      relies on the server-side guarantee, uses type casts
 *   - CLI:      calls schema.safeParse() directly where needed
 *   - Web:      relies on the server-side guarantee, uses type casts
 */

Issue raised with the help of Claude Code (claude-sonnet-4-6)