Create pr github

Create a GitHub pull request from the current branch using a description provided by the user.

$ARGUMENTS is the PR description — a sentence, bullet points, or a paragraph explaining what the PR does and why. If $ARGUMENTS is empty, ask the user to provide a description and stop.

Steps:

1. Check that gh is installed and authenticated by running gh auth status. If not, tell the user and stop.
2. Push the current branch to the remote if needed:
   • Run git rev-parse --abbrev-ref --symbolic-full-name @{upstream} to check if an upstream is set.
   • If no upstream is set, run git push -u origin HEAD to push and set tracking.
   • If an upstream is set, run git push to make sure the remote is up to date.
3. Derive a PR title (imperative tense, under 72 chars) and a polished description from $ARGUMENTS:
   • What changed (2-4 sentences, plain English)
   • Why it was needed if inferrable from the input
   • No filler like "This PR..." or vague words without specifics
4. Check if a PR already exists for this branch: gh pr view --json url,number 2>/dev/null.
   • If no PR exists, run gh pr create --title "<title>" --body "<description>" to open one.
   • If a PR already exists, run gh pr edit --title "<title>" --body "<description>" to update it.
5. Print the PR URL.