Line numbers in the diff gutter open a comment form on that line; every thread gets a reply fold. Both post to /mrs/{n}/diff-comment, which dispatches mr diff-comment.
No JavaScript — the anchor travels in the query (cpath/cline/cside).
Resolve controls were gated on write access while mr resolve also admits the thread author and the MR author; reviewRights now decides per thread.
Closes #44