Update project description for 1.4.0–1.5.1 capabilities

Problem/Motivation

The project description predates Audit Chain 1.4.0 through 1.5.1. It does not document scheduled verification, the keyed-assurance option, off-system evidence export, or the distinction between a broken seal and a foreign seal after a database refresh.

The encryption-profile guidance is also misleading: the evidence export excludes metadata, so exporting does not preserve encrypted metadata before a profile rotation.

Proposed resolution

• Keep the concise introduction, usage examples, collector guidance, and requirements.
• Document scheduled verification, health reporting, alerting, and the keyed-assurance option.
• Document verification-gated, data-minimized off-system export.
• Explain SEAL BROKEN versus fail-closed SEAL FOREIGN behavior.
• Direct profile rotation through drush audit-chain:reencrypt while the old profile remains available.

Remaining tasks

• Update the project description.
• Verify the rendered page, links, and requirements.

User interface changes

Documentation-only change to the Drupal.org project page.

API changes

None.

Data model changes

None.