Function merge 

pub fn merge(pr_number: usize) -> Result<()>

Merge a pull request using administrative squash semantics.

Invokes: gh pr merge --admin --squash --delete-branch <PR_NUMBER>.

Errors

• Spawning or executing the gh pr merge command fails.
• Command exits with non‑zero status (propagated by [ytil_cmd::CmdExt]).

Rationale

Squash + delete keeps history linear and prunes merged topic branches automatically.