feat(core): dev-only 'Open in DSL Playground' from visualizer

[thorthelegend99]

What this PR does

Adds a dev-mode only workflow to open visualized resources in the EventCatalog DSL Playground with one click.

Included

• New dev API route:
  • GET /api/dev/playground-export
  • Supports collections: services, events, commands, queries, domains
  • Loads the selected resource and exports hydrated DSL via SDK (toDSL(..., { hydrate: true }))
• Visualizer UI button (dev mode only):
  • Added to visualiser/[type]/[id]/[version]
  • Label: Open in DSL Playground (hydrated)
  • Fetches API DSL payload and opens https://playground.eventcatalog.dev/?dsl=...

Scope / guardrails

• This is intentionally dev mode only (isDevMode() check).
• No production/static-mode behavior changes in this PR.

Why

This provides a fast first step toward "export to playground" with minimal risk, while avoiding SSR/static rollout complexity in production.

Validation

• pnpm --filter @eventcatalog/core check

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Latest commit: f61da66

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