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/.env.example

@@ -0,0 +1,23 @@
+# API container.
+# Set API_BIND_ADDRESS to the Docker host interface reachable by the external
+# reverse proxy. Use 0.0.0.0 for LAN-wide exposure, or a specific host IP to
+# restrict where Docker publishes the port.
+API_BIND_ADDRESS=0.0.0.0
+API_PORT=8080
+MIGRATE_ON_STARTUP=true
+
+# PostgreSQL container bootstrap values. Replace the password before deploying.
+POSTGRES_DB=gametime
+POSTGRES_USER=gametime
+POSTGRES_PASSWORD=change-me
+
+# API database connection values. With this docker-compose.yaml, the database
+# host is the Compose service name `postgres`.
+DATABASE_HOST=postgres
+DATABASE_PORT=5432
+DATABASE_NAME=gametime
+DATABASE_USER=gametime
+DATABASE_PASSWORD=change-me
+
+# External HTTPS is terminated by a reverse proxy running outside this Compose
+# stack. Point that proxy to http://<docker-host>:${API_PORT}.