fix(golang-rewrite): print error message when app.Run fails

[teal-bauer]

Summary

• Print CLI error messages to stderr before exiting with error code

Previously, when app.Run() returned an error (e.g., asdf set -h foo 1.2.3), the CLI would exit with code 1 but print nothing, making it difficult to understand what went wrong.

Now the error message is printed (e.g., "No help topic for 'foo'").

Test plan

• Verify asdf set -h foo 1.2.3 now prints error message
• Verify asdf set -h still shows help with exit code 0
• Verify normal asdf set <tool> <version> still works
• Run existing CLI tests (go test ./internal/cli/...)

[teal-bauer]

I cannot count the number of times I have accidentally run asdf set -h foo 1.2.3 for home directory, where it would not show ANY error output, and then wonder why things didn't work, until at some point I remember to use -u instead. But I also always run asdf set --help, think "huh, but -h should've shown help but didn't, so maybe the -h did work...?"...

[teal-bauer]

Ping @asdf-vm/core?