Gmail connector: no tool to read or download email attachments

## Summary

The Gmail connector returns attachment metadata (filename, MIME type, attachment ID) but has no tool to retrieve attachment content. Claude can confirm an attachment exists but cannot read it.

## Reproduction

Asked Claude to interpret a levy notice from a strata manager. The email body was only "please find attached your Levy Notice"; every actionable detail — amounts, due dates, BPAY references, bank details — was in the attached PDF. Claude retrieved the message, confirmed the PDF attachment existed, and could go no further. The actual question was unanswerable.

## Impact

A large share of actionable email lives in attachments: invoices, statements, contracts, tickets, receipts, forms. Blocked tasks include "how much do I owe?", "when is this due?", "summarise this contract", "what's in the spreadsheet they sent?"

## Suggested improvement

A `get_attachment` tool taking message ID + attachment ID, returning base64 for binaries or extracted text for PDFs/documents. PDF-to-text extraction alone would cover most cases.