feat(frontend): add PL/EN i18n using @inlang/paraglide-js v2

- Install @inlang/paraglide-js v2 with Vite plugin and paraglideMiddleware hook
- Add messages/pl.json and messages/en.json with ~400 translation keys
- Create project.inlang/settings.json (PL as base locale)
- Add LanguageSwitcher component (cookie-based, no URL prefix needed)
- Replace all hardcoded strings across 14 pages/components with m.*() calls
- ProductForm uses derived label maps for all enum types (category, texture, etc.)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/hooks.server.ts

@@ -0,0 +1,6 @@
+import { paraglideMiddleware } from '$lib/paraglide/server.js';
+import type { Handle } from '@sveltejs/kit';
+
+export const handle: Handle = async ({ event, resolve }) => {
+	return paraglideMiddleware(event.request, () => resolve(event));
+};