Rewrite cosmetics and theme preferences (#1292)

- Cosmetics and theme preferences are now only stored in cookies instead
  of a combination of both cookies and state.

- The theme plugin now supports client hints. This allows the server
  to render a page using the client-preferred theme provided it supplies
  this information (any browser other than Firefox), helping to avoid an
  annoying flash while the page is hydrating.

- The previous workaround using the Nitro plugin has been removed. Its
  functionality is now handled by the Nuxt theme plugin with cleaner
  code.

- All pages and components now use the new plugins.

apps/frontend/src/composables/cosmetics.js

@@ -1,52 +0,0 @@
-export const useCosmetics = () =>
-  useState("cosmetics", () => {
-    const cosmetics = useCookie("cosmetics", {
-      maxAge: 60 * 60 * 24 * 365 * 10,
-      sameSite: "lax",
-      secure: true,
-      httpOnly: false,
-      path: "/",
-    });
-
-    if (!cosmetics.value) {
-      cosmetics.value = {
-        searchLayout: false,
-        projectLayout: false,
-        advancedRendering: true,
-        externalLinksNewTab: true,
-        notUsingBlockers: false,
-        hideModrinthAppPromos: false,
-        preferredDarkTheme: "dark",
-        searchDisplayMode: {
-          mod: "list",
-          plugin: "list",
-          resourcepack: "gallery",
-          modpack: "list",
-          shader: "gallery",
-          datapack: "list",
-          user: "list",
-          collection: "list",
-        },
-        hideStagingBanner: false,
-      };
-    }
-
-    return cosmetics.value;
-  });
-
-export const saveCosmetics = () => {
-  const cosmetics = useCosmetics();
-
-  console.log("SAVING COSMETICS:");
-  console.log(cosmetics);
-
-  const cosmeticsCookie = useCookie("cosmetics", {
-    maxAge: 60 * 60 * 24 * 365 * 10,
-    sameSite: "lax",
-    secure: true,
-    httpOnly: false,
-    path: "/",
-  });
-
-  cosmeticsCookie.value = cosmetics.value;
-};