[build] Rename trail audit_events -> audit_log; free name for domain Audit Event (AGREED)

[anmolg1997]

The product's Audit Event (a scoped audit run from a Profile) collides in name with our existing AuditEventRow (the 21 CFR Part 11 audit trail). Also 'Product Profile' vs our Product hierarchy entity. Pick distinct names (e.g. product entity AuditRun/audit_runs, or rename the trail to AuditTrailEvent) before building the product data model. See planning/RECONCILIATION.md (PR #156) for the full product↔engineering mapping.

[anmolg1997]

Both naming collisions confirmed — rename before building the product data models (RECONCILIATION §4.4):

1. Product "Audit Event" (the time-bound audit run, PLANNING_EVIDENCE_FEATURE_SPEC §1.1) vs our existing AuditEventRow — the 21 CFR Part 11 audit trail. Different concepts, same name. Suggested: product entity AuditRun/audit_runs, or rename the trail to AuditTrailEvent.
2. Product "Product Profile" (a Profile entity-type, PROFILES_FEATURE_SPEC §1.1) vs our existing Product hierarchy entity (Tenant→Site→Product).

Blocks the M2 (#159) data model — resolve before Sprint 2 entity work.

[anmolg1997]

AGREED (Akhilesh, per planning/architecture/02-DATA_ARCHITECTURE.md): the existing Part 11 trail — class AuditEventRow / table audit_events (backend/app/db/models/audit.py, writer audit/service.py:record_event) — is renamed to audit_log / AuditLogEntry, freeing the name for the new domain Audit Event entity. Concrete migration of shipped code; sequenced first in the data-layer build so the table name is free. Keep the trail's tenant_id non-FK (intentional — logs events before a tenant row exists).

[anmolg1997]

✅ Done — spec 013 (PR #238, merged → mvp-beta). Renamed audit_events→audit_log / AuditEventRow→AuditLogEntry; frees 'Audit Event' for the domain entity (spec 015).