feat(k8s): 新增 core 真应用(前端+Django API+Celery worker)构建与部署

- core/frontend: Vite 多阶段镜像 + nginx 同源反代 /api,/admin,/static(零 CORS)
- core/backend: Django gunicorn 镜像 + entrypoint(自动 migrate/collectstatic)+ WhiteNoise
- k8s/core: api/worker/web Deployment+Service + ingress(airshelf-web.airlabs.art)
- workflow: 追加 core 前后端 build/push,从 core/backend/.env 套生产覆盖生成 env Secret 后部署
- .gitignore 放行 core/backend/.env;.env 白名单加入 airshelf-web 域名
- 含前端 WIP 还原改动

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

core/backend/docker-entrypoint.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+set -e
+
+# Only the web (gunicorn) container should run migrations / collectstatic.
+# The celery worker shares this image but skips DB schema mutation to avoid races.
+case "$1" in
+  gunicorn)
+    echo "[entrypoint] running migrations..."
+    python manage.py migrate --noinput
+    echo "[entrypoint] collecting static..."
+    python manage.py collectstatic --noinput
+    ;;
+esac
+
+exec "$@"