docs: add Hlinor Mail Hub reference integration

[hlinor-systems]

Summary

Adds Hlinor Mail Hub as a reference communication source for ScopeGuard.

The documentation separates two distinct forms of evidence:

1. a real private Mail Hub integration proving provider-neutral event intake and replay behavior;
2. a public synthetic example demonstrating an actual scope-drift finding through the existing ScopeGuard engine.

Evidence

Verified behavior includes:

• six real messages from two selected chains imported through the private integration;
• repeat import produced zero new messages;
• review-only operation with no external writes;
• public synthetic reference tests: 2/2 PASS;
• one NEW DELIVERABLE finding in the excluded-dashboard scenario;
• stable finding identity on replay;
• zero findings when the dashboard is included in scope.

Scope

No private Operator implementation is included in this repository.

No live public Mail Hub connector, durable browser-side deduplication or enforcement capability is claimed.