fix(fedimint+home): guardian UI CSS resolves; quickstart goals full-width

- docker/fedimint-ui/nginx.conf: the local /assets/ handler 404'd the real
  fedimint guardian UI's own bundled CSS (bootstrap.min.css, style.css) →
  unstyled app. B13 fixed our local icon; this adds a @guardian_assets proxy
  fallback to :8177 so the guardian's own /assets/* resolve. Verified live on
  .116: /app/fedimint/assets/bootstrap.min.css 404→200 text/css. (needs
  archy-fedimint-ui image rebuild to persist on nodes.)
- Home.vue: Quick Start Goals card regained lg:col-span-2 so it fills its row
  on desktop instead of sitting at half width.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

neode-ui/src/views/Home.vue

@@ -231,7 +231,7 @@
         <!-- Quick Start Goals -->
         <div
           v-if="showQuickStart"
-          class="home-card transition-opacity duration-300"
+          class="home-card lg:col-span-2 transition-opacity duration-300"
           :class="{ 'home-card-animate': animateCards, 'opacity-0 pointer-events-none': showWelcomeBlock && !animateCards }"
           style="--card-stagger: 5"
         >