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)

markbase-core/Cargo.toml

@@ -68,9 +68,18 @@ ureq = "2.12"          # 輕量同步 HTTP 客戶端
 rayon = "1.10"          # Phase 4: 并行加密
 url = "2"              # URL 解析（rusty-s3 依賴）
 
+# === SMB/CIFS Client (Phase 1) ===
+smb2 = { path = "../vendor/smb2" }  # Pure-Rust SMB2/3 client library with pipelined I/O
+
+# === SMB/CIFS Server (Phase 2) — optional (vendored) ===
+smb-server = { path = "../vendor/smb-server", optional = true, default-features = false }
+async-trait = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+
 [features]
 default = []                          # 默认不启用可选格式
 optional-formats = ["unrar", "xz2", "sevenz-rust"]  # 争议格式可选启用
+smb-server = ["dep:smb-server"]       # SMB server feature flag
 
 [dev-dependencies]
 # tempfile moved to dependencies (needed for archive extraction)