Automatically reply to Gmail messages with full threading and recipient management.

• Handles message threading automatically by setting In-Reply-To, References, and threadId headers; quotes the original message in the reply
• Supports plain text and HTML reply bodies, with optional file attachments (multiple files via repeated --attach flags)
• Allows adding extra recipients via --to, --cc, and --bcc flags, or sending from an alias with --from
• Includes --dry-run mode to preview the request before sending, and --html flag for formatted replies with CSS styling