Text boxes: their typefaces count as used workbook fonts, so an installed one is bound; restore image_ext's doc comment (review fix-up for #401)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/ui-egui/src/lib.rs

@@ -300,6 +300,8 @@ impl SheetApp {
             names.extend(d.wb.styles.iter().map(|(_, s)| s.font.name.clone()));
             names.push(d.wb.theme.major_font.clone());
             names.push(d.wb.theme.minor_font.clone());
+            // Text boxes and shapes name their own typefaces.
+            names.extend(d.wb.sheets.iter().flat_map(|sh| sh.shapes.iter().filter_map(|s| s.format.font.clone())));
         }
         names
     }

crates/xlsx/src/drawing.rs

@@ -433,7 +433,6 @@ pub fn write_drawing(sheet: &Sheet, theme: &Theme, objs: &[Obj<'_>]) -> String {
     s
 }
 
-/// File extension for an image MIME type.
 /// A text run's `a:rPr` attributes (size, bold, italic) and children in schema order (outline,
 /// fill, typeface).
 fn run_props(f: &ShapeFormat, theme: &Theme) -> (String, String) {
@@ -463,6 +462,7 @@ fn run_props(f: &ShapeFormat, theme: &Theme) -> (String, String) {
     (attrs, body)
 }
 
+/// File extension for an image MIME type.
 pub fn image_ext(mime: &str, data: &[u8]) -> &'static str {
     match mime.to_ascii_lowercase().as_str() {
         "image/png" => "png",