test(platform): pin mailbox persistence boundaries

[yannickmonney]

What changed

• Add create/update regressions proving invalid mailbox ports are rejected before writes.
• Prove valid custom ports and declared defaults are stored.
• Pin served catalog metadata for IMAP/SMTP port constraints.

Verification

• Targeted type-aware Oxlint passed.
• Formatting, conflict-marker, and local SAST hooks passed.
• Targeted Vitest collection remains blocked by the environment's existing zod/v4 interop failure before tests execute.

Follow-up to merged PR #4260.

[yannickmonney]

Closing this redundant follow-up per independent review. PR #4260 already merged stronger create/update persistence regressions, served-catalog metadata coverage, and updated manual oracles at head 350ef72 (squash 080f87a). No additional source change is required. Real-browser evidence remains outstanding and is tracked on TALE-211.