feat: comprehensive metadata API schemas and integration tests for Hono, Next.js, NestJS

Expand metadata.zod.ts with full API contracts (CRUD, query, bulk, overlay,
import/export, validation, type registry, dependency tracking). Add
comprehensive integration tests for all three framework adapters.

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot