feat: add exact sender and domain filters

[cboone]

Problem

Current sender filtering is geared toward text search and can over/under-match during triage. Bulk processing works best with exact sender/domain criteria.

Proposal

Add explicit structured filters:

• --from-exact <email>
• --from-domain <domain>

Optional follow-up:

• --list-mail / --can-unsubscribe filters backed by email keywords for newsletter triage.

Acceptance Criteria

• Exact sender and domain filters are supported in search (and action-query mode if implemented).
• Matching is deterministic and case-insensitive for email/domain values.
• Docs include examples for sender/domain-based cleanup workflows.
• Tests cover exact address, domain-only, and combination with existing filters.

Notes

This reduces accidental over-selection and makes triage scripts robust.