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/package.json

@@ -26,6 +26,7 @@
 		"vite": "^7.3.1"
 	},
 	"dependencies": {
+		"@inlang/paraglide-js": "^2.13.0",
 		"bits-ui": "^2.16.2",
 		"clsx": "^2.1.1",
 		"lucide-svelte": "^0.575.0",