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/vite.config.ts

@@ -1,7 +1,12 @@
 import { sveltekit } from '@sveltejs/kit/vite';
 import tailwindcss from '@tailwindcss/vite';
 import { defineConfig } from 'vite';
+import { paraglideVitePlugin } from '@inlang/paraglide-js';
 
 export default defineConfig({
-	plugins: [tailwindcss(), sveltekit()]
+	plugins: [
+		paraglideVitePlugin({ project: './project.inlang', outdir: './src/lib/paraglide' }),
+		tailwindcss(),
+		sveltekit()
+	]
 });