fix: add missing secrets worker to repository

The secrets worker was being ignored due to broad gitignore pattern.
Added exception to allow workers/secrets/ directory while still ignoring actual secrets.

Files added:
- workers/secrets/Dockerfile
- workers/secrets/requirements.txt
- workers/secrets/worker.py

.gitignore

@@ -240,6 +240,10 @@ yarn-error.log*
 !**/secret_detection_benchmark_GROUND_TRUTH.json
 !**/secret_detection/results/
 
+# Exception: Allow workers/secrets/ directory (secrets detection worker)
+!workers/secrets/
+!workers/secrets/**
+
 secret*
 secrets/
 credentials*