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/vite.config.ts

@@ -1,5 +1,6 @@
 import { sveltekit } from '@sveltejs/kit/vite';
 import tailwindcss from '@tailwindcss/vite';
+import { paraglideVitePlugin as paraglide } from '@inlang/paraglide-js';
 import { defineConfig } from 'vite';
 
 // Source maps are always generated so that the CI pipeline can upload them to
@@ -8,7 +9,15 @@ export default defineConfig({
 	build: {
 		sourcemap: true
 	},
-	plugins: [tailwindcss(), sveltekit()],
+	plugins: [
+		tailwindcss(),
+		paraglide({
+			project: './project.inlang',
+			outdir: './src/lib/paraglide',
+			strategy: ['url', 'cookie', 'baseLocale']
+		}),
+		sveltekit()
+	],
 	ssr: {
 		// Force these packages to be bundled into the server output rather than
 		// treated as external requires. The production Docker image has no