feat(cli): add runtime package delegation

[tnez]

Summary

• Add runtime package manifest types and the public @tnezdev/agentic/runtime export path.
• Implement core runtime config registration, installed-package discovery, manifest validation, and delegation for runtime init/run/status.
• Cover missing, invalid, unknown, and installed runtime cases in CLI/config tests.

Closes #107

Test plan

• bun test
• bun run typecheck
• bun run build
• git diff --check