feat: disposable/temporary email detection

[polaz]

Summary

Detect temporary/disposable email domains (tempmail.com, guerrillamail.com, etc.). Feature-gated behind disposable flag.

Tasks

• Curate domain list from open-source sources (~3000 domains)
• Store as embedded sorted list + binary search (or trie if reusing PSL infra)
• email.is_disposable() -> bool
• Feature flag: disposable (not default — adds ~30KB)
• Test: known disposable domains detected, legitimate domains not flagged

Time estimate

3h