[backnotprop]

Answers plannotator/herdr-annotate#51 with a smaller feature: instead of editing inside the annotate pane, o opens the reviewed file in your own editor and reloads it when you come back.

• New rebindable action open-in-editor, default o (unused in every context; it sits in the global browse keys, so the keymap conflict check covers it).
• Uses $VISUAL, then $EDITOR; values with arguments work (code -w, nvim -u x, quoted paths). If neither is set, the footer says to set $EDITOR.
• File and folder reviews only. Reply and terminal reviews have no file, so the key just shows a short status.
• The TUI leaves the alternate screen and turns off raw mode, mouse capture, bracketed paste and the kitty keyboard flags. The editor then runs blocking in the same terminal, and all of that is restored afterwards. vim/nvim/nano/hx/emacs/micro/kak open at the current line via +N.
• If the file changed, it reloads the same way r does, so notes re-anchor. If it did not change (for example a GUI editor without its wait flag), nothing reloads and the existing "File changed on disk. Press r to reload." hint covers the later save.

Nothing changes for users who don't press the key.

Smoke-tested in tmux with an EDITOR script that recorded its argv and the terminal state, then edited the file. While the editor ran: +5 was passed, the tty was cooked (icanon/echo/isig) and alternate screen, mouse and paste were all off. Afterwards they were all back on, the file had reloaded and both notes re-anchored with 0 orphaned. I also checked a real vim -u NONE at the selected line, /usr/bin/true followed by a later external save (the hint appears and r reloads), no editor set, and a missing editor binary.