feat(T06): Mietkatalog frontend – equipment list, detail, search/filter, SSR

- composables/useApi.ts: base API client with runtimeConfig
- composables/useEquipment.ts: equipment API wrapper (list, detail, categories)
- components/EquipmentCard.vue: card with image/placeholder, badge, name, price, add-to-cart
- pages/mietkatalog.vue: SSR list with search, category chips, sort, pagination, skeleton, empty/error states
- pages/mietkatalog/[id].vue: SSR detail with specs table, related items, breadcrumb, add-to-cart
- nuxt.config.ts: runtimeConfig with apiBase
- 101 vitest tests passing (5 files)
- Build: 0 errors, 2.09 MB

frontend/nuxt.config.ts

@@ -50,6 +50,12 @@ export default defineNuxtConfig({
       ],
     },
   },
+  runtimeConfig: {
+    apiBase: process.env.API_BASE_URL || "http://localhost:8000",
+    public: {
+      apiBase: process.env.API_BASE_URL || "http://localhost:8000",
+    },
+  },
   routeRules: {
     "/mietkatalog": { ssr: true },
     "/mietkatalog/**": { ssr: true },