Implement VFS RAID-Z (software RAID)

- Add VfsRaidLevel enum:
  - Single (no RAID)
  - RaidZ1 (single parity, similar to RAID 5)
  - RaidZ2 (double parity, similar to RAID 6)
  - RaidZ3 (triple parity)
- Add VfsRaidBackend with:
  - Stripe-based data distribution across disks
  - Galois Field arithmetic for parity (P/Q/R)
  - gf_exp, gf_mul for Reed-Solomon coding
  - rebuild_disk() for disk recovery
- Add VfsRaidConfig:
  - level (RAID level)
  - stripe_size (default 64KB)
  - disk_paths (storage devices)
- All VfsBackend methods propagate to all disks
- Foundation for ZFS-style software RAID

All 229 tests pass.

markbase-core/src/vfs/mod.rs

@@ -2,6 +2,7 @@ pub mod compression;
 pub mod dedup;
 pub mod local_fs;
 pub mod open_flags;
+pub mod raid;
 pub mod s3_fs;
 pub mod smb_fs;
 #[cfg(feature = "smb-server")]
@@ -452,3 +453,48 @@ impl Default for VfsDedupConfig {
         }
     }
 }
+
+/// RAID级别（ZFS RAID-Z）
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum VfsRaidLevel {
+    /// 单磁盘（无RAID）
+    Single,
+    /// RAID-Z1（单奇偶校验，类似RAID 5）
+    RaidZ1,
+    /// RAID-Z2（双奇偶校验，类似RAID 6）
+    RaidZ2,
+    /// RAID-Z3（三奇偶校验）
+    RaidZ3,
+}
+
+impl std::fmt::Display for VfsRaidLevel {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            VfsRaidLevel::Single => write!(f, "Single"),
+            VfsRaidLevel::RaidZ1 => write!(f, "RAID-Z1"),
+            VfsRaidLevel::RaidZ2 => write!(f, "RAID-Z2"),
+            VfsRaidLevel::RaidZ3 => write!(f, "RAID-Z3"),
+        }
+    }
+}
+
+/// RAID配置
+#[derive(Debug, Clone)]
+pub struct VfsRaidConfig {
+    /// RAID级别
+    pub level: VfsRaidLevel,
+    /// 条带大小（字节），默认64KB
+    pub stripe_size: usize,
+    /// 磁盘列表路径
+    pub disk_paths: Vec<PathBuf>,
+}
+
+impl Default for VfsRaidConfig {
+    fn default() -> Self {
+        Self {
+            level: VfsRaidLevel::Single,
+            stripe_size: 65536,
+            disk_paths: Vec::new(),
+        }
+    }
+}