fix(cli): sanitize project argument newlines

[sentry]

This PR fixes an issue where parseOrgProjectArg would fail with a ValidationError: Invalid project slug: contains a newline. when given multi-line input.

Previously, parseOrgProjectArg only used arg.trim(), which removes leading/trailing whitespace but leaves internal newlines intact. This was particularly problematic for AI agents (e.g., Codex, Claude) that often pass arguments with appended output or notes after a newline (CLI-1RA).

The fix introduces a shared helper function, firstNonBlankLine, which extracts and returns only the first non-blank line from the input, trimming it. This aligns the behavior of parseOrgProjectArg with parseIssueArg, which already implemented similar logic to address a related issue (CLI-1G1).

This change ensures that project arguments are correctly sanitized, preventing crashes and improving the robustness of CLI commands that parse project identifiers.

Fixes CLI-1RA

_{@sentry <feedback>: Autofix iterates on these changes
@sentry stop iterating: Autofix stops iterating on this run}

_{This PR was automatically generated by Sentry. You can adjust this setting at any time.}