fix: respect the cursorline option across the pr surfaces

[undont]

Summary

• the diff painted its own cursor-line tint regardless of cursorline. _paint_cursorline now reads the window's effective value and returns early when it's off
• toggling cursorline mid-session left the tint on its last paint until the next cursor move; an OptionSet autocmd repaints on the spot
• the PR overview hardcoded cursorline off, so a cursorline user lost it; it now mirrors vim.go.cursorline
• the PR checks float set cursorline through a bare vim.wo[win], which writes the global too, switching the cursor line on for the rest of the session. it now goes through util.win.set_local like the other surfaces
• cursorline_tint's config comment said it "allows the cursorline to inherit" the highlights; it now says the tint is only drawn when cursorline is on
• the overview's g? cheatsheet and its two keymap comments used "review" for both the review screen and a github pending review, so e and r read as the same key. e is now enter, r is enter + start a draft review

Test plan

• make check clean