[verified] harden Sales Trainer and add PostgreSQL foundation

.dockerignore

@@ -1,12 +1,18 @@
-**/.venv/
-venv/
-**/__pycache__/
-*.pyc
-**/node_modules/
-backend/data/
-data/
+# Secrets and local state
 .env
+.env.*
+!.env.example
+backend/data/
+backend/.venv/
+
+# Build and tooling
+**/node_modules/
+frontend/dist/
+__pycache__/
+*.py[cod]
+.pytest_cache/
 **/*.log
 .DS_Store
-.git/
 .tmp/
+.git/
+.gitignore