feat(contacts): add feature flag to enable/disable exposition of users in address-book

src/common/config.rs

@@ -618,6 +618,9 @@ pub struct FeaturesConfig {
     pub enable_trash: bool,
     pub enable_search: bool,
     pub enable_music: bool,
+    /// Expose other OxiCloud users as a read-only "system" address book
+    /// at GET /api/address-books. Set to false to hide the user directory.
+    pub expose_system_users: bool,
 }
 
 impl Default for FeaturesConfig {
@@ -629,6 +632,7 @@ impl Default for FeaturesConfig {
             enable_trash: true,        // Enable trash feature
             enable_search: true,       // Enable search feature
             enable_music: true,        // Enable music feature
+            expose_system_users: true, // Expose OxiCloud users as address book by default
         }
     }
 }
@@ -948,6 +952,12 @@ impl AppConfig {
             config.features.enable_music = val;
         }
 
+        if let Ok(v) = env::var("OXICLOUD_EXPOSE_SYSTEM_USERS").map(|v| v.parse::<bool>())
+            && let Ok(val) = v
+        {
+            config.features.expose_system_users = val;
+        }
+
         // Storage limits
         if let Ok(max_upload) = env::var("OXICLOUD_MAX_UPLOAD_SIZE").map(|v| v.parse::<usize>())
             && let Ok(val) = max_upload