fix(cli): resolve plugins in Node SEA builds

[opencode-agent]

Summary

Node SEA's embedded ESM entrypoint does not provide import.meta.resolve, so plugin resolution throws before reaching the registered resolver hook.

• Obtain the native ESM resolver from a tiny module loaded through the existing VM-backed importer. Keep the synchronous API, package export conditions, parent-directory scope, and extension fallback unchanged.
• Exercise directory-plugin resolution in the existing compiled-service smoke test and require an active plugin, rather than merely a listed plugin. The previous standalone-file fixture bypassed resolution.

Validation

• Util: typecheck and all 47 tests pass.
• Plugin: typecheck and all 9 Host.resolve tests pass under Bun.
• The same 9 resolver tests pass as normal Node 26.4 ESM and as an actual SEA executable. Before the fix, all 9 SEA tests failed with TypeError: (intermediate value).resolve is not a function.
• CLI typecheck and changed-file formatting pass.
• Full CLI build/smoke remains unverified locally: bundling was OOM-killed by the host's per-command memory limit, including on the unchanged base. CI runs the full Node build and strengthened compiled-service smoke.

Requested by: @rekram1-node (Aiden via Slack)