CVE-2026-77258: MCP Atlassian: Arbitrary file read/exfiltration via upload_attachment missing validate_safe_path()

The upload_attachment method in confluence/attachments.py reads and uploads arbitrary local files to Confluence without calling validate_safe_path(). Both download methods (download_attachment at line 223, download_content_attachments at line 272) correctly call validate_safe_path() before writing files, but the upload path at lines 35-79 skips this check entirely.

An AI agent connected via MCP (or an attacker influencing that agent through prompt injection) can read any file on the host and exfiltrate it by uploading it as a Confluence page attachment.