ui: sidebar tab selector uses text labels instead of icons

The two drawn tab glyphs were judged not understandable enough; the
switcher goes to the wide policy with titles only, and the glyphs,
their gresource entries and the icon-naming code are removed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/ui_source.cpp

@@ -27,11 +27,9 @@ void build_source_panels(App& app) {
                                    GTK_POLICY_AUTOMATIC);
     gtk_scrolled_window_set_child(GTK_SCROLLED_WINDOW(scroller), p.widget);
     const std::string name = "source-" + p.id;
-    // An empty title on purpose, as for the built-in tabs: the pill is an icon, and
-    // `name_side_tabs()` puts `title` on it as tooltip and accessible name.
-    adw_view_stack_add_titled_with_icon(
-        ADW_VIEW_STACK(app.side_stack), scroller, name.c_str(), "",
-        p.icon.empty() ? "applications-engineering-symbolic" : p.icon.c_str());
+    // The tab is its title: the sidebar's pills are words, not glyphs.
+    adw_view_stack_add_titled(ADW_VIEW_STACK(app.side_stack), scroller, name.c_str(),
+                              p.title.c_str());
     app.source_panels.push_back({name, p.title, p.widget});
   }
   // Disconnected until the first Connected event says otherwise.