Move Docker files to docker/ directory

- Move Dockerfile, Dockerfile.base, docker-compose.yml to docker/
- Update docker-compose.yml with correct context paths
- Update scripts/build.sh to use new paths
- Update DOCKER_QUICKSTART.md with new commands
- Add scripts/build.sh to tracked files

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker/docker-compose.yml

@@ -0,0 +1,64 @@
+# Shared environment variables
+x-common-env: &common-env
+  STEGASOO_CHANNEL_KEY: ${STEGASOO_CHANNEL_KEY:-}
+
+services:
+  # ============================================================================
+  # Web UI (Flask)
+  # ============================================================================
+  web:
+    build:
+      context: ..
+      dockerfile: docker/Dockerfile
+      target: web
+    container_name: stegasoo-web
+    ports:
+      - "5000:5000"
+    environment:
+      <<: *common-env
+      FLASK_ENV: production
+      # Authentication (v4.0.2)
+      STEGASOO_AUTH_ENABLED: ${STEGASOO_AUTH_ENABLED:-true}
+      # HTTPS enabled by default - generates self-signed cert if none provided
+      # To disable: STEGASOO_HTTPS_ENABLED=false docker-compose up
+      STEGASOO_HTTPS_ENABLED: ${STEGASOO_HTTPS_ENABLED:-true}
+      STEGASOO_HOSTNAME: ${STEGASOO_HOSTNAME:-localhost}
+    volumes:
+      # Persist auth database and SSL certs (v4.0.2)
+      - stegasoo-web-data:/app/frontends/web/instance
+      - stegasoo-web-certs:/app/frontends/web/certs
+    restart: unless-stopped
+    deploy:
+      resources:
+        limits:
+          memory: 2048M
+        reservations:
+          memory: 1024M
+
+  # ============================================================================
+  # REST API (FastAPI)
+  # ============================================================================
+  api:
+    build:
+      context: ..
+      dockerfile: docker/Dockerfile
+      target: api
+    container_name: stegasoo-api
+    ports:
+      - "8000:8000"
+    environment:
+      <<: *common-env
+    restart: unless-stopped
+    deploy:
+      resources:
+        limits:
+          memory: 2048M
+        reservations:
+          memory: 1024M
+
+# Named volumes for persistent data
+volumes:
+  stegasoo-web-data:
+    driver: local
+  stegasoo-web-certs:
+    driver: local