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/server/plugins/theme.js

@@ -1,38 +0,0 @@
-export default defineNitroPlugin((nitroApp) => {
-  nitroApp.hooks.hook("render:html", (html, { event }) => {
-    try {
-      const cookies = parseCookies(event);
-
-      if (cookies && cookies["color-mode"]) {
-        const theme = JSON.parse(cookies["color-mode"]);
-
-        html.htmlAttrs.push(`class="${theme.value}-mode"`);
-      } else {
-        html.htmlAttrs.push(`class="dark-mode"`);
-      }
-
-      // Reset cookie attributes to correct ones
-      if (cookies) {
-        const opts = {
-          maxAge: 60 * 60 * 24 * 365 * 10,
-          sameSite: "lax",
-          secure: true,
-          httpOnly: false,
-          path: "/",
-        };
-
-        if (cookies["auth-token"]) {
-          setCookie(event, "auth-token", cookies["auth-token"], opts);
-        }
-        if (cookies["color-mode"]) {
-          setCookie(event, "color-mode", cookies["color-mode"], opts);
-        }
-        if (cookies.cosmetics) {
-          setCookie(event, "cosmetics", cookies.cosmetics, opts);
-        }
-      }
-    } catch (err) {
-      console.error(err);
-    }
-  });
-});