feat(i18n): add Paraglide i18n with 5 locales (v2.3.22)

- Install @inlang/paraglide-js v2.15.1; configure project.inlang settings
- Add en/ru/id/pt-BR/fr message catalogues (~140 keys each)
- Wire paraglideVitePlugin in vite.config.ts, reroute hook in hooks.ts,
  and paraglideHandle middleware in hooks.server.ts
- Migrate all routes and shared components to use m.*() message calls
- Fix duplicate onMount body in chapters/[n]/+page.svelte
- Build passes; svelte-check: 0 errors, 3 pre-existing warnings

ui/src/routes/admin/+layout.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
 	import { page } from '$app/state';
+	import * as m from '$lib/paraglide/messages.js';
 
 	const internalLinks = [
 		{ href: '/admin/scrape', label: 'Scrape' },
@@ -27,7 +28,7 @@
 	<aside class="w-48 shrink-0 border-r border-(--color-border) px-3 py-6 flex flex-col gap-6">
 		<!-- Internal pages -->
 		<div>
-			<p class="px-2 mb-2 text-xs font-semibold text-(--color-muted) uppercase tracking-widest">Pages</p>
+			<p class="px-2 mb-2 text-xs font-semibold text-(--color-muted) uppercase tracking-widest">{m.admin_pages_label()}</p>
 			<nav class="flex flex-col gap-0.5">
 				{#each internalLinks as link}
 					<a
@@ -45,7 +46,7 @@
 
 		<!-- External tools -->
 		<div>
-			<p class="px-2 mb-2 text-xs font-semibold text-(--color-muted) uppercase tracking-widest">Tools</p>
+			<p class="px-2 mb-2 text-xs font-semibold text-(--color-muted) uppercase tracking-widest">{m.admin_tools_label()}</p>
 			<nav class="flex flex-col gap-0.5">
 				{#each externalLinks as link}
 					<a