feat(server): packaging Docker Compose et push Gitea Registry (ticket #52)

Ajoute le Dockerfile multi-stage (build dart:stable, runtime
debian:bookworm-slim avec ca-certificates, exécutable AOT compilé), le
docker-compose.yaml (API + Postgres avec healthcheck et
depends_on: service_healthy), .env.example, .dockerignore et les
scripts scripts/docker-entrypoint.sh (migration au démarrage) et
scripts/push-gitea-image.sh (aucun identifiant en dur, mot de passe
via --password-stdin). dart analyze clean, dart test 24/24 vert,
`docker compose config` valide (syntaxe, interpolation de variables,
healthcheck). Dockerfile et scripts relus manuellement et jugés
corrects ; pas de docker build/compose up réel faute d'accès au
daemon Docker dans ce sandbox.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/Dockerfile

@@ -0,0 +1,33 @@
+FROM dart:stable AS build
+
+WORKDIR /app
+
+COPY pubspec.* ./
+RUN dart pub get
+
+COPY . .
+RUN dart compile exe bin/server.dart -o build/server \
+    && dart compile exe bin/migrate.dart -o build/migrate
+
+FROM debian:bookworm-slim AS runtime
+
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+
+ENV PORT=8080
+ENV MIGRATE_ON_STARTUP=true
+
+COPY --from=build /app/build/server /app/bin/server
+COPY --from=build /app/build/migrate /app/bin/migrate
+COPY migrations/ /app/migrations/
+COPY scripts/docker-entrypoint.sh /app/scripts/docker-entrypoint.sh
+
+RUN chmod +x /app/bin/server /app/bin/migrate /app/scripts/docker-entrypoint.sh
+
+EXPOSE 8080
+
+ENTRYPOINT ["/app/scripts/docker-entrypoint.sh"]
+CMD ["/app/bin/server"]