SMB Server Phase 2: VFS backend build fix + integration test

- Add VfsFile: Send supertrait for Mutex compatibility
- Fix SmbServerCommand: struct → Subcommand enum with Start variant
- Fix tracing_subscriber::init() → try_init() to avoid panic when
  logger already initialized
- Fix CLI subcommand name: smb-server → smb-start (flatten naming)
- Add #[command(name = "smb-start")] for CLI disambiguation
- Fix unused variable warnings (smb_fs.rs, smb_server_backend.rs)
- Remove unused VfsFile imports (webdav.rs, scp_handler.rs)
- Integration test: Docker smbclient verified (list, upload, read)

AGENTS.md

@@ -2925,3 +2925,26 @@ cargo test -p markbase-core --lib  # ✅ 157 passed, 0 failed
 
 **最后更新**：2026-06-20 14:45
 **版本**：1.33（Web Frontend Phase 3 完成）
+
+---
+
+## SMB Server Phase 2 Build Fix（2026-06-20）⭐⭐⭐⭐⭐
+
+**完成时间**：约 30 分钟
+
+### 修复内容 ⭐⭐⭐⭐⭐
+
+1. **`VfsFile` trait 添加 `Send` supertrait**：`vfs/mod.rs` — 所有实现已经是 `Send`，显式约束无需 unsafe cast
+2. **`SmbServerCommand` 改为 enum**：`smb_server.rs` — 使用 `#[derive(Subcommand)]` 枚举（`Start` 变体）以兼容 `#[command(flatten)]`
+3. **`smb_server_backend.rs` 测试修复**：用 `matches!(result, Err(SmbError::NotFound))` 替代 `result.unwrap_err()` 避免 `Debug` 约束
+4. **移除未使用 `VfsFile` import**：`webdav.rs` + `scp_handler.rs`
+
+### 验证 ✅
+
+```bash
+cargo build -p markbase-core --features smb-server      # ✅ 0 error
+cargo test -p markbase-core --lib --features smb-server  # ✅ 169 passed, 0 failed
+cargo build -p markbase-core                              # ✅ 0 error (no features)
+```
+
+**版本**：1.34（SMB Server Phase 2 Build Fix）