v1.7.0: fix offer created_at override, invoice PDF translations, remove has_order filter

- Add created_at to offer create/update schemas so user-selected date is stored instead of always defaulting to now()
- Translate payment method in invoice PDF based on language (Příkazem → Bank transfer, etc.)
- Add order_date and cnb_rate translation keys, replace hardcoded inline strings
- Remove duplicate has_order filter from offers backend route

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "app-ts",
-  "version": "1.6.9",
+  "version": "1.7.0",
   "description": "",
   "main": "dist/server.js",
   "scripts": {