P1: AsyncSmbVfs implementation (Phase 4)

- AsyncSmbVfs: spawn_blocking wrapper over SmbVfs
- AsyncSmbFile: tokio::sync::Mutex for async state
- Add Clone derive to SmbVfs (Arc<Mutex<Tree>>)
- Remove manual Clone impl (derive handles it)

Phase 4 complete: AsyncSmbVfs working
Phase 5 pending: WebDAV integration

Tests: 293 passed, 0 failed

markbase-core/src/vfs/smb_fs.rs

@@ -39,10 +39,11 @@ fn map_smb_error(e: smb2::Error) -> VfsError {
 }
 
 /// SMB 客户端 VFS 后端 (SMB 2/3)
+#[derive(Clone)]
 pub struct SmbVfs {
     runtime: Arc<tokio::runtime::Runtime>,
     client: Arc<Mutex<smb2::SmbClient>>,
-    tree: Mutex<smb2::Tree>,
+    tree: Arc<Mutex<smb2::Tree>>,
 }
 
 impl SmbVfs {
@@ -90,7 +91,7 @@ impl SmbVfs {
         Ok(Self {
             runtime,
             client: Arc::new(Mutex::new(client)),
-            tree: Mutex::new(tree),
+            tree: Arc::new(Mutex::new(tree)),
         })
     }
 
@@ -100,16 +101,6 @@ impl SmbVfs {
     }
 }
 
-impl Clone for SmbVfs {
-    fn clone(&self) -> Self {
-        Self {
-            runtime: self.runtime.clone(),
-            client: self.client.clone(),
-            tree: Mutex::new(self.tree.lock().unwrap().clone()),
-        }
-    }
-}
-
 impl VfsBackend for SmbVfs {
     fn clone_boxed(&self) -> Box<dyn VfsBackend> {
         Box::new(self.clone())