feat: Add mark_emails tool for batch read/unread/flag operations

[patrickfreyer]

Summary

Add a tool to batch mark emails as read, unread, flagged, or unflagged based on criteria.

Motivation

Currently there's no way to mark emails as read after viewing them. This is the most basic email action and completes the "find → view → act" loop.

Proposed API

@mcp.tool()
def mark_emails(
    account: str,
    action: Literal["read", "unread", "flagged", "unflagged"],
    subject_keyword: Optional[str] = None,
    sender: Optional[str] = None,
    mailbox: str = "INBOX",
    max_emails: int = 10
) -> str:
    """Batch mark emails based on criteria."""

Use Cases

• "Mark all newsletters as read"
• "Flag emails from my manager"
• "Mark all emails older than 7 days as read"

Priority

HIGH - Most requested missing action

Labels

enhancement, priority-high