close stdin and exit cleanly when ai setup init fails

[sentry-junior]

• ai-assisted setup can fail with Failed to analyze project structure: Forbidden
• when setup fails, the terminal session can remain stuck instead of exiting cleanly
• likely related behavior from thread context: stdin appears to be closed explicitly on successful init completion, but not on failure paths

steps observed:

• start the setup wizard that analyzes the project and configures Sentry
• hit a failure during analysis with Forbidden
• after the failure, the terminal remains stuck

notes:

• the Forbidden error itself was resolved separately
• the remaining bug is the terminal/escape behavior after a failed init path

this issue is intentionally sanitized and excludes personal or thread-specific details.