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/hooks.server.ts

@@ -1,4 +1,5 @@
 import type { Handle } from '@sveltejs/kit';
+import { sequence } from '@sveltejs/kit/hooks';
 import { handleErrorWithSentry } from '@sentry/sveltekit';
 import * as Sentry from '@sentry/sveltekit';
 import { randomBytes, createHmac } from 'node:crypto';
@@ -13,6 +14,7 @@ import { OTLPLogExporter } from '@opentelemetry/exporter-logs-otlp-http';
 import { BatchLogRecordProcessor } from '@opentelemetry/sdk-logs';
 import { resourceFromAttributes } from '@opentelemetry/resources';
 import { ATTR_SERVICE_NAME, ATTR_SERVICE_VERSION } from '@opentelemetry/semantic-conventions';
+import { paraglideMiddleware } from '$lib/paraglide/server';
 
 // ─── OpenTelemetry server-side tracing + logs ─────────────────────────────────
 // No-op when OTEL_EXPORTER_OTLP_ENDPOINT is unset (e.g. local dev).
@@ -138,7 +140,21 @@ export function parseAuthToken(token: string): { id: string; username: string; r
 
 // ─── Hook ─────────────────────────────────────────────────────────────────────
 
-export const handle: Handle = async ({ event, resolve }) => {
+function getTextDirection(locale: string): string {
+	// All supported locales (en, ru, id, pt-BR, fr) are LTR
+	return 'ltr';
+}
+
+const paraglideHandle: Handle = ({ event, resolve }) =>
+	paraglideMiddleware(event.request, ({ request: localizedRequest, locale }) => {
+		event.request = localizedRequest;
+		return resolve(event, {
+			transformPageChunk: ({ html }) =>
+				html.replace('%lang%', locale).replace('%dir%', getTextDirection(locale))
+		});
+	});
+
+const appHandle: Handle = async ({ event, resolve }) => {
 	// During graceful shutdown, reject new requests immediately so the load
 	// balancer / Docker health-check can drain existing connections.
 	if (shuttingDown) {
@@ -197,3 +213,5 @@ export const handle: Handle = async ({ event, resolve }) => {
 	return resolve(event);
 };
 
+export const handle = sequence(paraglideHandle, appHandle);
+