Add --output-folder flag to gotap run

[mmaelicke]

Summary

gorun currently writes outputs to the default /out mount when invoking gotap run, because gotap does not yet support an explicit --output-folder flag.

Why this matters

Supporting --output-folder would make the shim contract clearer and let callers choose a non-default output location without relying on implicit behavior.

Context

While testing gorun on March 18, 2026, a run failed with:

Error: unknown flag: --output-folder

We removed the flag from gorun for now because /out is already the default, but we still want to add the flag to gotap later.

Follow-up

• add --output-folder to gotap run
• keep /out as the default when the flag is omitted
• document the behavior in the CLI help and README