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/jest.config.mjs

@@ -0,0 +1,21 @@
+/** @type {import('ts-jest').JestConfigWithTsJest} */
+export default {
+  preset: "ts-jest/presets/default-esm",
+  testEnvironment: "node",
+  roots: ["<rootDir>/src"],
+  moduleNameMapper: {
+    "^(\\.{1,2}/.*)\\.js$": "$1",
+  },
+  transform: {
+    "^.+\\.tsx?$": [
+      "ts-jest",
+      {
+        useESM: true,
+      },
+    ],
+  },
+  extensionsToTreatAsEsm: [".ts"],
+  collectCoverageFrom: ["src/**/*.ts", "!src/**/*.test.ts"],
+  coverageDirectory: "coverage",
+  coverageReporters: ["text", "lcov", "clover"],
+};