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/tests/medication_tests.rs

@@ -8,9 +8,9 @@
 mod medication_tests {
     use reqwest::Client;
     use serde_json::json;
-    
+
     const BASE_URL: &str = "http://localhost:3000";
-    
+
     #[tokio::test]
     async fn test_create_medication_requires_auth() {
         let client = Client::new();
@@ -25,11 +25,11 @@ mod medication_tests {
             .send()
             .await
             .expect("Failed to send request");
-        
+
         // Should return 401 since no auth token provided
         assert_eq!(response.status(), 401);
     }
-    
+
     #[tokio::test]
     async fn test_list_medications_requires_auth() {
         let client = Client::new();
@@ -38,20 +38,23 @@ mod medication_tests {
             .send()
             .await
             .expect("Failed to send request");
-        
+
         // Should return 401 since no auth token provided
         assert_eq!(response.status(), 401);
     }
-    
+
     #[tokio::test]
     async fn test_get_medication_requires_auth() {
         let client = Client::new();
         let response = client
-            .get(&format!("{}/api/medications/507f1f77bcf86cd799439011", BASE_URL))
+            .get(&format!(
+                "{}/api/medications/507f1f77bcf86cd799439011",
+                BASE_URL
+            ))
             .send()
             .await
             .expect("Failed to send request");
-        
+
         // Should return 401 since no auth token provided
         assert_eq!(response.status(), 401);
     }