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>

.husky/pre-commit

@@ -1,16 +1,16 @@
 #!/bin/sh
 
 # Check if backend files changed
-if git diff --cached --name-only | grep -q "^website-monitoring-backend/"; then
+if git diff --cached --name-only | grep -q "^backend/"; then
   echo "🔍 Linting backend..."
-  cd website-monitoring-backend && npx eslint src/ || exit 1
+  cd backend && npx eslint src/ || exit 1
   cd ..
 fi
 
 # Check if frontend files changed
-if git diff --cached --name-only | grep -q "^website-monitoring-frontend/"; then
+if git diff --cached --name-only | grep -q "^frontend/"; then
   echo "🔍 Linting frontend..."
-  cd website-monitoring-frontend && npx next lint || exit 1
+  cd frontend && npx next lint || exit 1
   cd ..
 fi