fix(infra): make MEILI_URL configurable; rename Discover → Catalogue in nav

- docker-compose.yml: MEILI_URL in x-infra-env was hardcoded to the local
  meilisearch container, ignoring the Doppler MEILI_URL secret entirely.
  Changed to "${MEILI_URL:-http://meilisearch:7700}" so prod reads from
  https://search.libnovel.cc while local dev keeps the container default.
- ui/+layout.svelte: rename nav + footer label from "Discover" to "Catalogue"
  (desktop nav, mobile menu, footer — all three occurrences).

ui/src/routes/+layout.svelte

@@ -244,7 +244,7 @@
 				href="/catalogue"
 				class="hidden sm:block text-sm transition-colors {page.url.pathname.startsWith('/catalogue') ? 'text-zinc-100 font-medium' : 'text-zinc-400 hover:text-zinc-100'}"
 			>
-				Discover
+				Catalogue
 			</a>
 			<a
 				href="https://feedback.libnovel.cc"
@@ -332,7 +332,7 @@
 				onclick={() => (menuOpen = false)}
 				class="px-3 py-2.5 rounded-lg text-sm font-medium transition-colors {page.url.pathname.startsWith('/catalogue') ? 'bg-zinc-800 text-zinc-100' : 'text-zinc-400 hover:bg-zinc-800 hover:text-zinc-100'}"
 			>
-				Discover
+				Catalogue
 			</a>
 			<a
 				href="https://feedback.libnovel.cc"
@@ -400,7 +400,7 @@
 			<!-- Top row: site links -->
 			<nav class="flex flex-wrap items-center justify-center gap-x-5 gap-y-2">
 			<a href="/books" class="hover:text-zinc-400 transition-colors">Library</a>
-			<a href="/catalogue" class="hover:text-zinc-400 transition-colors">Discover</a>
+			<a href="/catalogue" class="hover:text-zinc-400 transition-colors">Catalogue</a>
 			<a
 				href="https://feedback.libnovel.cc"
 				target="_blank"