refactor: flatten monorepo structure to backend/ frontend/ devops/

Rename subdirectories for a cleaner single-repo layout:
- website-monitoring-backend/  → backend/
- website-monitoring-frontend/ → frontend/
- website-monitoring-devops/   → devops/

Update all references in package.json scripts, CI workflows,
docker-compose, pre-commit hooks, and documentation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/tsconfig.json

@@ -0,0 +1,14 @@
+// filepath: /c:/Users/denni/OneDrive/Dokumente/code/website-monitoring/backend/tsconfig.json
+{
+  "compilerOptions": {
+    "module": "ESNext",
+    "target": "es2018",
+    "moduleResolution": "node",
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "strict": true,
+    "forceConsistentCasingInFileNames": true,
+    "outDir": "./dist"
+  },
+  "include": ["src"]
+}