Add SMB AAPL Extensions Phase 1-6 + VFS xattr support

Phase 1: AAPL Create Context negotiation
Phase 2: AFP_AfpInfo Stream structure (Finder info + creation time)
Phase 2.5: SMB Named Stream Backend (NamedStreamPath)
Phase 2.6: Backend Named Stream Support in handlers
Phase 2.7: VFS Extended Attributes (get/set/remove/list_xattr)
Phase 4: Time Machine share config (time_machine field)
Phase 5: Server/Volume Capabilities
Phase 6: macOS Unicode mapping (private range ↔ ASCII)

Tests: 174 smb-server tests pass, 52 VFS tests pass

markbase-core/src/vfs/mod.rs

@@ -327,6 +327,28 @@ pub trait VfsBackend: Send + Sync {
     fn remove_ace(&self, _path: &Path, _ace_index: usize) -> Result<(), VfsError> {
         Err(VfsError::Unsupported("remove_ace".to_string()))
     }
+
+    // ===== Extended Attributes (xattr) support =====
+
+    /// 获取扩展属性
+    fn get_xattr(&self, _path: &Path, _name: &str) -> Result<Vec<u8>, VfsError> {
+        Err(VfsError::Unsupported("get_xattr".to_string()))
+    }
+
+    /// 设置扩展属性
+    fn set_xattr(&self, _path: &Path, _name: &str, _value: &[u8]) -> Result<(), VfsError> {
+        Err(VfsError::Unsupported("set_xattr".to_string()))
+    }
+
+    /// 删除扩展属性
+    fn remove_xattr(&self, _path: &Path, _name: &str) -> Result<(), VfsError> {
+        Err(VfsError::Unsupported("remove_xattr".to_string()))
+    }
+
+    /// 列出扩展属性名称
+    fn list_xattrs(&self, _path: &Path) -> Result<Vec<String>, VfsError> {
+        Err(VfsError::Unsupported("list_xattrs".to_string()))
+    }
 }
 
 /// 快照信息