fix(frontend): Step3 - Amélioration genre + ajout fichiers Docker

- Suppression label 'Genre', boutons radio centrés (Fille/Garçon)
- Réduction espacements pour éviter dépassement
- Ajout docker-compose.yml et Dockerfiles depuis master

Ticket #38

frontend/Dockerfile

@@ -0,0 +1,16 @@
+# Stage builder
+FROM ghcr.io/cirruslabs/flutter:3.19.0 AS builder
+WORKDIR /app
+COPY pubspec.* ./
+RUN flutter pub get
+COPY . .
+RUN flutter build web --release
+
+# Stage production
+FROM nginx:alpine
+COPY nginx.conf /etc/nginx/conf.d/default.conf
+COPY --from=builder /app/build/web /usr/share/nginx/html
+
+EXPOSE 80
+
+CMD ["nginx", "-g", "daemon off;"]