MCP Add get_attachments tool

Tool: get_attachment (VIEW, on by default)
Metadata header always (mimetype, size, attachment version, author, date, document version, download URL), then dispatch by mimetype:

• text-like -> inline under the 6000-token budget with offset
• PDF/office -> Tika extraction, labeled
• images ≤ 2 MB png/jpeg/gif/webp -> real image content block
• everything else -> metadata + URL.