feat(api): Add audit logging for all operations

[pparage]

Context

No audit trail exists for API operations. Cannot determine who deployed/deleted/modified what and when.

Requirements

• Log every mutating API call with: timestamp, operation, parameters, user/source, outcome
• Store in persistent database
• GET /v0/admin/audit — Query audit log with filtering

Dependencies

Requires persistence layer (B1).

Priority

Nice-to-have.

References

• Gap analysis: gap-analysis.md issue B17