Create Issue Branch Github

Create a branch linked to a GitHub issue and check it out locally.

$ARGUMENTS is the issue number. If $ARGUMENTS is empty, ask the user to provide an issue number and stop.

Steps:

1. Check that gh is installed and authenticated by running gh auth status. If not, tell the user and stop.
2. Run gh issue view $ARGUMENTS --json title,state to confirm the issue exists. If it doesn't exist or is already closed, tell the user and stop.
3. Check if gh issue develop is available by running gh issue develop --help 2>/dev/null. Then:
   • If available: Run gh issue develop $ARGUMENTS --checkout. Pass --name <name> if a custom name was provided in $ARGUMENTS. GitHub names the branch <number>-<issue-title-slug> automatically and links it to the issue.
   • If not available (older gh): Derive the branch name from the issue number and title: lowercase the title, replace spaces and special characters with hyphens, truncate to ~5 words, and prefix with the issue number (e.g. 12-add-decision-command). Run git checkout -b <branch-name>.
4. Tell the user the branch name and confirm they are now on it.
   • If gh issue develop was used: note that the branch is linked to the issue and will appear in the issue's Development sidebar automatically.
   • If the fallback was used: note that gh issue develop requires gh v2.11+ and suggest upgrading. Advise adding Closes #<number> to the PR description to link the issue when opening a PR.