SMB CLI: Add S3 VFS backend support (--s3 flag)

Usage:
  smb-start --s3     --s3-endpoint https://s3.example.com     --s3-bucket mybucket     --s3-access-key AKIA...     --s3-secret-key secret...

All SMB operations now work over S3-compatible storage.

All 229 tests pass.

markbase-core/src/cli/tools/smb_server.rs

@@ -18,6 +18,24 @@ pub enum SmbServerCommand {
 
         #[arg(short, long, value_parser = parse_user)]
         user: Vec<(String, String)>,
+
+        #[arg(long)]
+        s3: bool,
+
+        #[arg(long)]
+        s3_endpoint: Option<String>,
+
+        #[arg(long)]
+        s3_bucket: Option<String>,
+
+        #[arg(long)]
+        s3_access_key: Option<String>,
+
+        #[arg(long)]
+        s3_secret_key: Option<String>,
+
+        #[arg(long, default_value = "us-east-1")]
+        s3_region: String,
     },
 }
 
@@ -39,6 +57,12 @@ pub async fn handle_smb_server_command(cmd: SmbServerCommand) -> anyhow::Result<
                 share_name,
                 read_only,
                 user,
+                s3,
+                s3_endpoint,
+                s3_bucket,
+                s3_access_key,
+                s3_secret_key,
+                s3_region,
             } => {
                 use std::path::PathBuf;
 
@@ -55,7 +79,29 @@ pub async fn handle_smb_server_command(cmd: SmbServerCommand) -> anyhow::Result<
                 let addr: std::net::SocketAddr = format!("0.0.0.0:{}", port).parse()?;
                 let root_path = PathBuf::from(&root);
 
-                let vfs = Box::new(crate::vfs::local_fs::LocalFs::new());
+                let vfs: Box<dyn crate::vfs::VfsBackend> = if s3 {
+                    let endpoint = s3_endpoint
+                        .ok_or_else(|| anyhow::anyhow!("--s3-endpoint required when --s3 is enabled"))?;
+                    let bucket = s3_bucket
+                        .ok_or_else(|| anyhow::anyhow!("--s3-bucket required when --s3 is enabled"))?;
+                    let access_key = s3_access_key
+                        .ok_or_else(|| anyhow::anyhow!("--s3-access-key required when --s3 is enabled"))?;
+                    let secret_key = s3_secret_key
+                        .ok_or_else(|| anyhow::anyhow!("--s3-secret-key required when --s3 is enabled"))?;
+
+                    log::info!("S3 backend: endpoint={}, bucket={}, region={}", endpoint, bucket, s3_region);
+
+                    Box::new(crate::vfs::s3_fs::S3Vfs::new(
+                        &endpoint,
+                        &s3_region,
+                        &bucket,
+                        &access_key,
+                        &secret_key,
+                    )?)
+                } else {
+                    Box::new(crate::vfs::local_fs::LocalFs::new())
+                };
+
                 let backend = crate::vfs::smb_server_backend::VfsShareBackend::new(vfs, root_path)
                     .read_only(read_only);