Fix panic on non-ASCII thread titles in archive search
Richard Feldman
created
The archive view's fuzzy_match_positions used chars().enumerate()
which produces character indices, not byte indices. When thread titles
contain multi-byte UTF-8 characters (emoji, CJK, etc.), these character
indices don't correspond to valid byte boundaries, causing a panic in
HighlightedLabel::new.
Switch to char_indices() and eq_ignore_ascii_case() to produce correct
byte positions, matching the approach used by the sidebar's version of
the same function.