Rename .title CSS class to .page-title to avoid libadwaita collision

bread-theme's shared .title rule (1.4em bold) was a bare class selector
that also matched libadwaita's internal row/window-title labels, which
carry the same "title" class. That's what inflated breadman's settings
row titles to ~24px. Scoping the name to .page-title here (the only
consumer of the old class) and bumping bread-theme to the dev branch
where the rename lives.

src/ui/guide_view.rs

@@ -8,7 +8,7 @@ pub fn build(store: &ContentStore, guide: &Guide, simplified: bool, binds: &[Key
     vbox.add_css_class("view-content");
 
     let title = Label::new(Some(&guide.meta.title));
-    title.add_css_class("title");
+    title.add_css_class("page-title");
     title.set_xalign(0.0);
     vbox.append(&title);