Fix SFTP file upload failures with JWT filer tokens (#8448)

* Fix SFTP file upload failures with JWT filer tokens (issue #8425)

When JWT authentication is enabled for filer operations via jwt.filer_signing.*
configuration, SFTP server file upload requests were rejected because they lacked
JWT authorization headers.

Changes:
- Added JWT signing key and expiration fields to SftpServer struct
- Modified putFile() to generate and include JWT tokens in upload requests
- Enhanced SFTPServiceOptions with JWT configuration fields
- Updated SFTP command startup to load and pass JWT config to service

This allows SFTP uploads to authenticate with JWT-enabled filers, consistent
with how other SeaweedFS components (S3 API, file browser) handle filer auth.

Fixes #8425

* Apply suggestion from @gemini-code-assist[bot]

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

weed/sftpd/sftp_service.go

@@ -47,6 +47,10 @@ type SFTPServiceOptions struct {
 
 	// User Management
 	UserStoreFile string // Path to user store file
+
+	// JWT Configuration for Filer
+	FilerSigningKey          []byte // JWT signing key for filer uploads
+	FilerSigningExpiresAfter int    // JWT token expiration time in seconds
 }
 
 // NewSFTPService creates a new service instance.
@@ -201,6 +205,8 @@ func (s *SFTPService) handleSSHConnection(conn net.Conn, config *ssh.ServerConfi
 		s.options.DataCenter,
 		s.options.FilerGroup,
 		sftpUser,
+		s.options.FilerSigningKey,
+		s.options.FilerSigningExpiresAfter,
 	)
 
 	// Ensure home directory exists with proper permissions