fix: render hint labels and correct match column offsets

[bigboss2063]

Issue #1668: hint labels not showing up

• Wire hint_labels through PanelFrame into build_row_bg (paints hint_background on labeled cells) and build_row_fg (new emit_hint_label_glyphs phase shapes each label char as a one-cell run and overlays it in hint_foreground, drawn last so it replaces the underlying matched text). The configured hint_foreground / hint_background colors were defined but read by no renderer.

Byte-offset-as-column drift on lines with non-ASCII cells

• find_regex_matches and find_regex_match_at_point converted oniguruma byte offsets to column indices via char count. The previous Column(byte) drifted matches rightward on lines containing non-ASCII cells (e.g. nerd-font PUA icons from oh-my-posh prompts), breaking highlight/label placement and mouse-hover hit-testing. Copy/Command actions still worked because they use the text field, not the Pos.

Stale hint_labels during search

• update_hint_state now clears hint_labels whenever hint mode is inactive (not only when search is also inactive); previously leftover labels could be drawn over search results once the label renderer was wired in.

Fix result (using the same configuration as in the issue)

Before：

After：