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/handlers/permissions.rs

@@ -2,15 +2,11 @@ use axum::{
     extract::{Query, State},
     http::StatusCode,
     response::IntoResponse,
-    Json,
-    Extension,
+    Extension, Json,
 };
 use serde::{Deserialize, Serialize};
 
-use crate::{
-    auth::jwt::Claims,
-    config::AppState,
-};
+use crate::{auth::jwt::Claims, config::AppState};
 
 #[derive(Debug, Deserialize)]
 pub struct CheckPermissionQuery {
@@ -32,27 +28,35 @@ pub async fn check_permission(
     Query(params): Query<CheckPermissionQuery>,
     Extension(claims): Extension<Claims>,
 ) -> impl IntoResponse {
-    let has_permission = match state.db.check_user_permission(
-        &claims.sub,
-        &params.resource_type,
-        &params.resource_id,
-        &params.permission,
-    ).await {
+    let has_permission = match state
+        .db
+        .check_user_permission(
+            &claims.sub,
+            &params.resource_type,
+            &params.resource_id,
+            &params.permission,
+        )
+        .await
+    {
         Ok(result) => result,
         Err(e) => {
             tracing::error!("Failed to check permission: {}", e);
-            return (StatusCode::INTERNAL_SERVER_ERROR, Json(serde_json::json!({
-                "error": "failed to check permission"
-            }))).into_response();
+            return (
+                StatusCode::INTERNAL_SERVER_ERROR,
+                Json(serde_json::json!({
+                    "error": "failed to check permission"
+                })),
+            )
+                .into_response();
         }
     };
-    
+
     let response = PermissionCheckResponse {
         has_permission,
         resource_type: params.resource_type,
         resource_id: params.resource_id,
         permission: params.permission,
     };
-    
+
     (StatusCode::OK, Json(response)).into_response()
 }