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>

frontend/.eslintrc.json

@@ -0,0 +1,10 @@
+{
+  "extends": ["next/core-web-vitals"],
+  "rules": {
+    "@typescript-eslint/no-explicit-any": "off",
+    "@typescript-eslint/no-unused-vars": ["warn", { "argsIgnorePattern": "^_", "varsIgnorePattern": "^_" }],
+    "react-hooks/exhaustive-deps": "warn",
+    "react/no-unescaped-entities": "off",
+    "@next/next/no-img-element": "warn"
+  }
+}