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/Dockerfile

@@ -0,0 +1,38 @@
+# --- Stage 1: Dependencies ---
+FROM node:20-slim AS deps
+WORKDIR /app
+COPY package.json package-lock.json ./
+RUN npm ci
+
+# --- Stage 2: Build ---
+FROM node:20-slim AS builder
+WORKDIR /app
+COPY --from=deps /app/node_modules ./node_modules
+COPY . .
+ENV NEXT_TELEMETRY_DISABLED=1
+ENV TAILWIND_DISABLE_OXIDE=1
+RUN npm run build
+
+# --- Stage 3: Production ---
+FROM node:20-slim AS runtime
+WORKDIR /app
+
+RUN groupadd -r app && useradd -r -g app -d /app app
+
+COPY --from=builder --chown=app:app /app/.next/standalone ./
+COPY --from=builder --chown=app:app /app/.next/static ./.next/static
+COPY --from=builder --chown=app:app /app/public ./public
+
+USER app
+
+EXPOSE 3000
+
+ENV PORT=3000
+ENV HOSTNAME="0.0.0.0"
+ENV NODE_ENV=production
+ENV NEXT_TELEMETRY_DISABLED=1
+
+HEALTHCHECK --interval=30s --timeout=5s --start-period=30s --retries=3 \
+  CMD node -e "const h=require('http');h.get('http://localhost:3000/api/health',(r)=>{process.exit(r.statusCode===200?0:1)}).on('error',()=>process.exit(1))"
+
+CMD ["node", "server.js"]