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/scripts/push-gitea-image.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+require_env() {
+  local name="$1"
+  if [[ -z "${!name:-}" ]]; then
+    echo "Missing required environment variable: ${name}" >&2
+    exit 1
+  fi
+}
+
+require_env GITEA_REGISTRY
+require_env GITEA_OWNER
+require_env GITEA_IMAGE_NAME
+require_env GITEA_USERNAME
+require_env GITEA_TOKEN
+
+GITEA_IMAGE_TAG="${GITEA_IMAGE_TAG:-latest}"
+IMAGE_REF="${GITEA_REGISTRY}/${GITEA_OWNER}/${GITEA_IMAGE_NAME}:${GITEA_IMAGE_TAG}"
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+SERVER_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"
+
+docker build -t "${IMAGE_REF}" "${SERVER_DIR}"
+printf '%s' "${GITEA_TOKEN}" | docker login "${GITEA_REGISTRY}" \
+  --username "${GITEA_USERNAME}" \
+  --password-stdin
+docker push "${IMAGE_REF}"
+
+echo "Pushed ${IMAGE_REF}"