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>

app/ui/BillEditForm.tsx

@@ -202,6 +202,16 @@ export const BillEditForm:FC<BillEditFormProps> = ({ location, bill }) => {
                     ))}
                 </div>
 
+                {/* Show toggle only when adding a new bill (not editing) */}
+                {!bill && (
+                    <div className="form-control mt-4">
+                        <label className="label cursor-pointer">
+                            <span className="label-text">{t("add-to-subsequent-months")}</span> 
+                            <input type="checkbox" name="addToSubsequentMonths" className="toggle toggle-primary" />
+                        </label>
+                    </div>
+                )}
+
                 <div className="pt-4">
                     <button type="submit" className="btn btn-primary">{t("save-button")}</button>
                     <Link className="btn btn-neutral ml-3" href={`/?year=${billYear}&month=${billMonth}`}>{t("cancel-button")}</Link>