v1.6.0: fix offer items mobile layout and localStorage draft save/restore

- Fix items table description column width on mobile (was ~82px, now ~260px)
- Activate unused offers-items-table CSS class in OfferDetail form
- Save all form fields to localStorage draft (language, VAT, exchange rate were missing)
- Use DRAFT_KEY constant in loadOfferDraft, add error logging

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "app-ts",
-  "version": "1.5.9",
+  "version": "1.6.0",
   "description": "",
   "main": "dist/server.js",
   "scripts": {