refactor: improve type safety in MongoDB operations

Add TypeScript generic type parameters to MongoDB collection calls and
remove ObjectId conversion workaround.

Changes:
- Added <BillingLocation> type parameter to collection().updateOne() calls
- Simplified _id usage by removing new ObjectId() conversion
- Cleaner code with better type inference

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

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

email-worker/src/lib/emailSenders.ts

@@ -69,8 +69,8 @@ export async function sendVerificationRequests(db: Db, budget: number): Promise<
 
         // Update location status
         const newStatus = success ? EmailStatus.VerificationPending : EmailStatus.VerificationFailed;
-        await db.collection('lokacije').updateOne(
-            { _id: new ObjectId(location._id as any) },
+        await db.collection<BillingLocation>('lokacije').updateOne(
+            { _id: location._id },
             { $set: { tenantEmailStatus: newStatus } }
         );
 
@@ -171,8 +171,8 @@ export async function sendRentDueNotifications(db: Db, budget: number): Promise<
 
         // Update location status
         const newStatus = success ? 'sent' : 'failed';
-        await db.collection('lokacije').updateOne(
-            { _id: new ObjectId(location._id as any) },
+        await db.collection<BillingLocation>('lokacije').updateOne(
+            { _id: location._id },
             { $set: { rentDueNotificationStatus: newStatus } }
         );
 
@@ -264,8 +264,8 @@ export async function sendUtilityBillsNotifications(db: Db, budget: number): Pro
 
         // Update location status
         const newStatus = success ? 'sent' : 'failed';
-        await db.collection('lokacije').updateOne(
-            { _id: new ObjectId(location._id as any) },
+        await db.collection<BillingLocation>('lokacije').updateOne(
+            { _id: location._id },
             { $set: { billFwdStatus: newStatus } }
         );