feat: add OpenCode 2 (V2) plugin entrypoint

[danielxxomg]

Description

OpenCode 2 loads plugins as { id, setup } through ctx.catalog.transform. Support the ./v2 export to allow native integration without manual provider blocks.

Context

Collaborator PR upstream: brent-weatherall#15 by @Majidalee1

[danielxxomg]

Resolved in commit eaca63c: added v2.ts exporting OpenCode 2 plugin { id, setup } with ctx.catalog.transform and ./v2 package export.