feat(audit): implement audit logging for search requests and results

- Added configuration options for audit database path and retention days in backend and processor.
- Integrated audit logging in server and worker processes to track search requests, completions, and failures.
- Created utility functions for reading and parsing audit logs in end-to-end tests.
- Updated Docker Compose files to include audit database configuration.
- Added new tests to verify audit log entries for successful and no-results searches.

stacks/faceai.yml

@@ -24,6 +24,8 @@ services:
       FACEAI_RUNTIME_ROOT: /data/runtime
       FACEAI_UPLOAD_ROOT: /data/runtime/uploads
       FACEAI_LOG_ROOT: /data/logs
+      FACEAI_AUDIT_DB_PATH: /data/logs/faceai-audit.sqlite
+      FACEAI_AUDIT_RETENTION_DAYS: 730
       FACEAI_PKL_ROOT: /data/pkl
       FACEAI_ENABLE_LOCAL_LEGACY_STATIC: 0
     volumes:
@@ -59,6 +61,8 @@ services:
       FACEAI_QUEUE_NAME: faceai-searches
       FACEAI_RUNTIME_ROOT: /data/runtime
       FACEAI_LOG_ROOT: /data/logs
+      FACEAI_AUDIT_DB_PATH: /data/logs/faceai-audit.sqlite
+      FACEAI_AUDIT_RETENTION_DAYS: 730
       FACEAI_PKL_ROOT: /data/pkl
       FACEAI_MATCHER_BINARY: /app/bin/face_matcher
       FACEAI_MATCHER_TOLERANCE: 0.5