refactor: improve notification naming and introduce type-safe enums

- Rename billFwd* to billsNotification* for clarity
- Rename rentDueNotification* to rentNotification* for consistency
- Rename utilBillsProofOfPayment to billsProofOfPayment
- Introduce enums for type safety:
  - BillsNotificationStrategy (WhenPayed, WhenAttached)
  - BillsNotificationStatus (Scheduled, Sent, Failed)
  - RentNotificationStatus (Sent, Failed)
- Replace "pending" status with "scheduled" for better semantics
- Fix function names to proper camelCase
- Fix incorrect import path in web-app/app/lib/format.ts

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

web-app/app/lib/actions/monthActions.ts

@@ -2,13 +2,13 @@
 
 import { getDbClient } from '../dbClient';
 import { ObjectId } from 'mongodb';
-import { Bill, BillingLocation, YearMonth } from '@evidencija-rezija/shared-code';
+import { Bill, BillingLocation, BillsNotificationStatus, YearMonth } from '@evidencija-rezija/shared-code';
 import { AuthenticatedUser } from '../types/next-auth';
 import { withUser } from '../auth';
 import { unstable_noStore as noStore, unstable_noStore, revalidatePath } from 'next/cache';
 import { getLocale } from 'next-intl/server';
 import { gotoHomeWithMessage } from './navigationActions';
-import { shouldUpdateBillFwdStatusWhenPayed } from '../billForwardingHelpers';
+import { shouldUpdateBillsNotificationStatusWhenPayed } from '../billForwardingHelpers';
 
 /**
  * Server-side action which adds a new month to the database
@@ -44,7 +44,7 @@ export const addMonth = withUser(async (user:AuthenticatedUser, { year, month }:
             ...prevLocation,
             // clear properties specific to the month
             seenByTenantAt: undefined,
-            utilBillsProofOfPayment: undefined,
+            billsProofOfPayment: undefined,
             // assign a new ID
             _id: (new ObjectId()).toHexString(),
             yearMonth: {
@@ -234,11 +234,11 @@ export const updateMonth = withUser(async (
             // Check if any paid bill triggers forwarding (only need to check once)
             const firstPaidUpdate = locationUpdates.find(update => update.paid === true);
             
-            if (firstPaidUpdate && shouldUpdateBillFwdStatusWhenPayed(location, firstPaidUpdate.billId, true)) {
-                // Update billFwdStatus to "pending"
+            if (firstPaidUpdate && shouldUpdateBillsNotificationStatusWhenPayed(location, firstPaidUpdate.billId, true)) {
+                // Update billsNotificationStatus to "scheduled"
                 await dbClient.collection<BillingLocation>("lokacije").updateOne(
                     { _id: locationId },
-                    { $set: { billFwdStatus: "pending" } }
+                    { $set: { billsNotificationStatus: BillsNotificationStatus.Scheduled } }
                 );
             }
         }