add bulk bill creation across subsequent months

Implement ability to add newly created bills to all subsequent months
with toggle option (disabled by default). Includes duplicate checking
and efficient bulk operations.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

messages/hr.json

@@ -77,6 +77,7 @@
     "save-button": "Spremi",
     "cancel-button": "Odbaci",
     "delete-tooltip": "Obriši račun",
+    "add-to-subsequent-months": "Dodaj u sve mjesece koji slijede",
     "validation": {
       "bill-name-required": "Ime računa je obavezno",
       "not-a-number": "Vrijednost mora biti brojka",