Add test infrastructure and example vault content

- Add docker-compose.test.yml for isolated testing
- Add test vault with sample Markdown notes across categories
- Add frontend audit script for module validation
- Increment user failed_attempts in test data

test-vault/subfolder/Document caché.md

@@ -0,0 +1,7 @@
+---
+tags: [caché, test]
+---
+
+# Document dans un sous-dossier
+
+Ce document teste l'arborescence.