Problem: email-quoted diffs (`> diff --git ...`, `> @@ ...`) from
git-send-email workflows produce 0 hunks because the parser matches
patterns against raw lines containing `> ` quote prefixes.
Solution: strip quote prefix before pattern matching in the parser,
store `quote_width` on each hunk, offset all extmark column positions
by `qw` in `highlight.lua`, and expand `pw > 1` guards to
`qw > 0 or pw > 1` for DiffsClear suppression. Clamp body prefix
DiffsClear `end_col` to actual buffer line length for bare `>` lines
where `nvim_buf_set_extmark` would reject out-of-range columns.
