Reduce database load from dashboard polling and correct activity reporting

[javuto]

Summary

Reduce database load from polling and live event streams, and correct enrollment activity reporting.

• Remove routine read audits while preserving mutation, download, and security events.
• Add configurable audit retention, defaulting to 90 days, with bounded cleanup batches.
• Count successful enrollments explicitly and classify query actions correctly.
• Cache permissions per request and stream authorization pass while preserving revocation checks.
• Safely remove redundant status/result UUID indexes without changing existing column types.

Validation

• Full Go test suite passed.
• TypeScript checks and audit-page tests passed.
• OpenAPI check passed.
• Added regression tests for retention, enrollment classification, permission revocation, and index upgrades.
• Live MySQL/PostgreSQL migration tests were skipped because test databases were unavailable.

Operational notes

Audit cleanup runs at API startup and hourly. Configure a longer retention period before rollout if needed. Historical enrollment counts are not reconstructed from generic node audit rows.