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/tour/callout.rs

@@ -72,7 +72,7 @@ pub fn build(
     root.set_size_request(CALLOUT_WIDTH, -1);
 
     let title = Label::new(Some(&step.title));
-    title.add_css_class("title");
+    title.add_css_class("page-title");
     title.set_xalign(0.0);
     title.set_wrap(true);
     root.append(&title);