AgenticMail API/storage and outbound relay hardening fixes

The current upstream main branch at commit 7e0206d was reviewed, and the fix-first patch set was rebased on 2026-05-18. The patches cover: validated and bound inactive-agent hour filtering; storage SQL identifier validation; metadata-backed ownership checks for raw storage SQL; blocking direct storage metadata access through raw SQL; fail-closed outbound worker secret handling; SMTP envelope/header control-character validation before command construction; and TLS certificate verification as the default for MailSender with an explicit opt-out for local development. Validation completed locally with targeted API/Core security tests plus API/Core builds. The security patch branch was not published publicly because te repository's SECURITY.md asks reporters not to open public vulnerability issues.