docs(docs): add header tabs for Changelog and Appendix pages

apps/docs/blume.config.ts

@@ -142,8 +142,11 @@ export default defineConfig({
     sidebar: {
       display: "flat", // "flat" | "group" | "page"
     },
-    // No `featured`: Blume renders it above the `Sidebar` slot, and the
-    // content-source selector must sit above the pinned links, so
-    // components/SourceSidebar.astro renders both (Changelog, Appendix).
+    // The two custom pages (pages/*.astro) as header tabs. Neither is a
+    // content folder, so the tabs scope nothing out of the sidebar tree.
+    tabs: [
+      { label: "Changelog", path: "/changelog", icon: "clock" },
+      { label: "Appendix", path: "/appendix", icon: "library" },
+    ],
   },
 });