feat: clarify Draco export ownership

[alexchuber]

Summary

• replace the misleading raw-encoder connection payload with typed per-export compression options
• keep encoder preparation, extension registration, and Draco activation inside the opt-in block
• keep glTF output neutral and preserve per-export compression isolation
• split connection-point definitions by payload, colocate block infrastructure, and flatten the core node asset modules

Validation

• 8/8 focused code-review agents completed on the Draco ownership changes
• fixed the shared runtime guard ownership finding
• pnpm test (59 tests)
• pnpm format:check
• pnpm lint
• pnpm build
• git diff --check