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/models/share.rs

@@ -1,7 +1,7 @@
+use mongodb::bson::DateTime;
 use mongodb::bson::{doc, oid::ObjectId};
 use mongodb::Collection;
 use serde::{Deserialize, Serialize};
-use mongodb::bson::DateTime;
 
 use super::permission::Permission;
 
@@ -42,7 +42,7 @@ impl Share {
             active: true,
         }
     }
-    
+
     pub fn is_expired(&self) -> bool {
         if let Some(expires) = self.expires_at {
             DateTime::now() > expires
@@ -50,11 +50,11 @@ impl Share {
             false
         }
     }
-    
+
     pub fn has_permission(&self, permission: &Permission) -> bool {
         self.permissions.contains(permission) || self.permissions.contains(&Permission::Admin)
     }
-    
+
     pub fn revoke(&mut self) {
         self.active = false;
     }
@@ -69,19 +69,19 @@ impl ShareRepository {
     pub fn new(collection: Collection<Share>) -> Self {
         Self { collection }
     }
-    
+
     pub async fn create(&self, share: &Share) -> mongodb::error::Result<Option<ObjectId>> {
         let result = self.collection.insert_one(share, None).await?;
         Ok(Some(result.inserted_id.as_object_id().unwrap()))
     }
-    
+
     pub async fn find_by_id(&self, id: &ObjectId) -> mongodb::error::Result<Option<Share>> {
         self.collection.find_one(doc! { "_id": id }, None).await
     }
-    
+
     pub async fn find_by_owner(&self, owner_id: &ObjectId) -> mongodb::error::Result<Vec<Share>> {
         use futures::stream::TryStreamExt;
-        
+
         self.collection
             .find(doc! { "owner_id": owner_id }, None)
             .await?
@@ -89,27 +89,37 @@ impl ShareRepository {
             .await
             .map_err(|e| mongodb::error::Error::from(e))
     }
-    
-    pub async fn find_by_target(&self, target_user_id: &ObjectId) -> mongodb::error::Result<Vec<Share>> {
+
+    pub async fn find_by_target(
+        &self,
+        target_user_id: &ObjectId,
+    ) -> mongodb::error::Result<Vec<Share>> {
         use futures::stream::TryStreamExt;
-        
+
         self.collection
-            .find(doc! { "target_user_id": target_user_id, "active": true }, None)
+            .find(
+                doc! { "target_user_id": target_user_id, "active": true },
+                None,
+            )
             .await?
             .try_collect()
             .await
             .map_err(|e| mongodb::error::Error::from(e))
     }
-    
+
     pub async fn update(&self, share: &Share) -> mongodb::error::Result<()> {
         if let Some(id) = &share.id {
-            self.collection.replace_one(doc! { "_id": id }, share, None).await?;
+            self.collection
+                .replace_one(doc! { "_id": id }, share, None)
+                .await?;
         }
         Ok(())
     }
-    
+
     pub async fn delete(&self, share_id: &ObjectId) -> mongodb::error::Result<()> {
-        self.collection.delete_one(doc! { "_id": share_id }, None).await?;
+        self.collection
+            .delete_one(doc! { "_id": share_id }, None)
+            .await?;
         Ok(())
     }
 }