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/docker-compose.yaml

@@ -0,0 +1,42 @@
+services:
+  api:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    restart: unless-stopped
+    depends_on:
+      postgres:
+        condition: service_healthy
+    environment:
+      PORT: 8080
+      MIGRATE_ON_STARTUP: ${MIGRATE_ON_STARTUP:?set MIGRATE_ON_STARTUP}
+      DATABASE_HOST: ${DATABASE_HOST:?set DATABASE_HOST}
+      DATABASE_PORT: ${DATABASE_PORT:?set DATABASE_PORT}
+      DATABASE_NAME: ${DATABASE_NAME:?set DATABASE_NAME}
+      DATABASE_USER: ${DATABASE_USER:?set DATABASE_USER}
+      DATABASE_PASSWORD: ${DATABASE_PASSWORD:?set DATABASE_PASSWORD}
+    ports:
+      - "${API_BIND_ADDRESS:?set API_BIND_ADDRESS}:${API_PORT:?set API_PORT}:8080"
+
+  postgres:
+    image: postgres:16-alpine
+    restart: unless-stopped
+    environment:
+      POSTGRES_DB: ${POSTGRES_DB:?set POSTGRES_DB}
+      POSTGRES_USER: ${POSTGRES_USER:?set POSTGRES_USER}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:?set POSTGRES_PASSWORD}
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+    healthcheck:
+      test:
+        [
+          "CMD-SHELL",
+          "pg_isready -U \"$${POSTGRES_USER}\" -d \"$${POSTGRES_DB}\""
+        ]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+      start_period: 10s
+
+volumes:
+  postgres_data: