Implement WebDAV VFS integration: dav-server 0.11 compatible

- Add webdav.rs module: VfsDavFs, VfsDavFile, VfsDavMetaData
- Implement DavFileSystem + Clone for GuardedFileSystem blanket impl
- Add clone_boxed to VfsBackend trait (required for Sync)
- Update CLI webdav.rs to use VFS instead of SQLite
- Add bytes dependency
- All 155 tests pass

markbase-core/Cargo.toml

@@ -18,6 +18,7 @@ sevenz-rust = { version = "0.6.1", optional = true }     # 7z格式 ⚠️库不
 anyhow = "1"
 axum = { version = "0.7", features = ["macros"] }
 bcrypt = "0.16"
+bytes = "1"
 chrono = { version = "0.4", features = ["serde"] }
 regex = "1"
 clap = { version = "4", features = ["derive"] }
@@ -26,7 +27,6 @@ filetree = { path = "../filetree" }
 futures-util = "0.3"
 log = "0.4"
 env_logger = "0.11"
-markbase-webdav = { path = "../markbase-webdav" }
 pulldown-cmark = "0.12"
 rusqlite = { version = "0.32", features = ["bundled"] }
 sled = "1.0.0-alpha.124"