WebDAV improvements: flush fix, RwLock recovery, expired lock cleanup, atomic set_times

P0 fixes:
- flush(): add flushed flag, proper error logging, Drop warning for data loss
- props_data RwLock: replace unwrap() with try_read/try_write recovery
- PersistedLs: add is_expired() + cleanup_expired_locks() helper

P1 improvements:
- Props persistence via VFS (load_props/save_props/patch_props)
- COPY/MOVE sync dead props (copy on COPY, move key on rename)
- Atomic set_atime/set_mtime via filetime crate (no race condition)

New files:
- webdav_locks.rs: PersistedLs with lock persistence + expiry cleanup

Tests: 288 passed, 0 failed

markbase-core/src/vfs/mod.rs

@@ -148,6 +148,21 @@ pub trait VfsBackend: Send + Sync {
     /// 删除空目录
     fn remove_dir(&self, path: &Path) -> Result<(), VfsError>;
 
+    /// 递归删除目录及其所有内容
+    fn remove_dir_all(&self, path: &Path) -> Result<(), VfsError> {
+        // Default: read entries and remove one by one
+        let entries = self.read_dir(path)?;
+        for entry in entries {
+            let child = path.join(&entry.name);
+            if entry.stat.is_dir {
+                self.remove_dir_all(&child)?;
+            } else {
+                self.remove_file(&child)?;
+            }
+        }
+        self.remove_dir(path)
+    }
+
     /// 删除文件
     fn remove_file(&self, path: &Path) -> Result<(), VfsError>;
 
@@ -157,6 +172,28 @@ pub trait VfsBackend: Send + Sync {
     /// 设置文件属性
     fn set_stat(&self, path: &Path, stat: &VfsStat) -> Result<(), VfsError>;
 
+    /// 原子性设置 atime 和 mtime（默认实现调用 stat + set_stat，有 race condition）
+    fn set_times(&self, path: &Path, atime: SystemTime, mtime: SystemTime) -> Result<(), VfsError> {
+        let mut stat = self.stat(path)?;
+        stat.atime = atime;
+        stat.mtime = mtime;
+        self.set_stat(path, &stat)
+    }
+
+    /// 原子性设置 atime（默认实现调用 stat + set_stat，有 race condition）
+    fn set_atime(&self, path: &Path, atime: SystemTime) -> Result<(), VfsError> {
+        let mut stat = self.stat(path)?;
+        stat.atime = atime;
+        self.set_stat(path, &stat)
+    }
+
+    /// 原子性设置 mtime（默认实现调用 stat + set_stat，有 race condition）
+    fn set_mtime(&self, path: &Path, mtime: SystemTime) -> Result<(), VfsError> {
+        let mut stat = self.stat(path)?;
+        stat.mtime = mtime;
+        self.set_stat(path, &stat)
+    }
+
     /// 读取符号链接目标
     fn read_link(&self, path: &Path) -> Result<PathBuf, VfsError>;
 
@@ -172,6 +209,24 @@ pub trait VfsBackend: Send + Sync {
     /// 创建硬链接
     fn hard_link(&self, original: &Path, link: &Path) -> Result<(), VfsError>;
 
+    /// 复制文件（高效实现，fallback 到 read+write）
+    fn copy(&self, from: &Path, to: &Path) -> Result<(), VfsError> {
+        let flags = open_flags::OpenFlags::new().read();
+        let mut src = self.open_file(from, &flags)?;
+        let write_flags = open_flags::OpenFlags::new().write().create().truncate().mode(0o644);
+        let mut dst = self.open_file(to, &write_flags)?;
+        let mut buf = vec![0u8; 65536];
+        loop {
+            match src.read(&mut buf) {
+                Ok(0) => break,
+                Ok(n) => dst.write_all(&buf[..n])?,
+                Err(e) => return Err(e),
+            }
+        }
+        dst.flush()?;
+        Ok(())
+    }
+
     // ===== Snapshot support (ZFS-style) =====
 
     /// 创建快照