apply boxdraw patch for perfect box-drawing character alignment

Applied st-boxdraw_v2-0.8.5.diff with manual adjustments for st 0.9:
- Added boxdraw.c to build sources
- Added ATTR_BOXDRAW attribute flag (bit 13, after ATTR_SELECTED)
- Integrated boxdraw detection in tsetchar() function
- Modified xmakeglyphfontspecs() to use boxdraw for applicable characters
- Adjusted indentation for harfbuzz integration compatibility

Benefits:
- Box-drawing characters now align perfectly regardless of font
- Improved visual quality for tmux, tree, dialog output
- Covers Unicode U2500-U259F (lines/blocks) and U28XX (braille)

1 files changed, 3 insertions, 0 deletions

diff --git a/st.c b/st.c
index fe54b95..57feebb 100644
--- a/st.c
+++ b/st.c
@@ -1446,6 +1446,9 @@ tsetchar(Rune u, const Glyph *attr, int x, int y)
 	term.line[y][x] = *attr;
 	term.line[y][x].u = u;
 	term.line[y][x].mode |= ATTR_SET;
+
+	if (isboxdraw(u))
+		term.line[y][x].mode |= ATTR_BOXDRAW;
 }
 
 void