Email health checks are now real, not estimated.

• Live mail server tests: STARTTLS, certificate validity and expiry, banner, and an open relay check run against your actual MX hosts.
• Finds DKIM automatically across 40+ common selectors and flags wildcard records.
• One consistent score across the app and dnskit.dev, with clearer OK / warning / error states.
• SPF lookup count and DMARC policy details in the results.
• When a test cannot run, it is marked skipped instead of guessed.
• Fixes and performance improvements.