fix: opencode run shouldn't print to stderr

[veracioux]

Relates to #369 (comment)
Tested by:

opencode run hi

Hi! How can I help with your software engineering tasks?

$

opencode run hi | cat
Hi! How can I help with your software engineering tasks?
$

$ opencode run hi 2>/dev/null
Hi! How can I help with your software engineering tasks?
$

$ opencode run hi >/dev/null
$

$ opencode run hi --print-logs --format=json | jq
... prints correct output and jq doesn't print any errors ...
$