style: apply rustfmt to backend codebase

- Apply rustfmt to all Rust source files in backend/
- Fix trailing whitespace inconsistencies
- Standardize formatting across handlers, models, and services
- Improve code readability with consistent formatting

These changes are purely stylistic and do not affect functionality.
All CI checks now pass with proper formatting.

backend/src/security/audit_logger.rs

@@ -1,6 +1,6 @@
+use crate::models::audit_log::{AuditEventType, AuditLog, AuditLogRepository};
 use anyhow::Result;
 use mongodb::bson::oid::ObjectId;
-use crate::models::audit_log::{AuditLog, AuditLogRepository, AuditEventType};
 
 #[derive(Clone)]
 pub struct AuditLogger {
@@ -24,7 +24,14 @@ impl AuditLogger {
         resource_id: Option<String>,
     ) -> Result<ObjectId> {
         self.repository
-            .log(event_type, user_id, email, ip_address, resource_type, resource_id)
+            .log(
+                event_type,
+                user_id,
+                email,
+                ip_address,
+                resource_type,
+                resource_id,
+            )
             .await
     }