062f85cf1b
Add MergePull HTTP handler that calls the existing client.MergePull()
method, register the POST /pulls/{owner}/{repo}/{index}/merge route,
and add a merge button/form to the PR detail template gated on
Mergeable and open state. Supports merge, rebase, and squash styles.
- Handler returns HTMX fragment on HX-Request, redirect otherwise
- Error path returns inline error fragment for HTMX requests
- Add mock merge endpoint and 3 integration tests
- Merge button only shows when PR is mergeable and open
Closes leeworks-agents/gitea-mobile#229
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>