补充测试覆盖率 + 新增部署引导命令 bootstrap_deployment

- 新增 apps/blog、apps/solutions、apps/home、apps/api 测试文件，覆盖标签/排序/
  草稿过滤、HomePage.subpage_types 回归测试、page_preview 预览接口
- apps/core/tests.py 新增健康检查端点、发布 webhook 信号、bootstrap_deployment
  命令的测试用例，pytest 用例数从 40 增至 65，全部通过
- 修复 apps/api/urls.py 中 PagePreviewAPIViewSet.get_object() 未捕获
  DoesNotExist 导致 500 而非文档承诺 404 的 bug
- 新增 apps/core/management/commands/bootstrap_deployment.py：部署时按环境变量
  幂等创建首个超级管理员账号并联动初始化 RBAC 权限组，.env.example 补充对应
  环境变量说明
- 新增 OpenSearch + 中文分词本地 PoC 脚手架（docker-compose.opensearch.yml +
  docker/opensearch/Dockerfile），调研结论详见设计文档 §2.10
- 更新设计文档 §2.16 Phase 1 进度清单

apps/api/tests.py

@@ -0,0 +1,47 @@
+"""apps.api 单元测试：预览专用接口 `page_preview`（apps/api/urls.py 的
+PagePreviewAPIViewSet），覆盖 §2.7/§2.15 描述的"仅凭有效 content_type+token
+才能读取草稿快照"行为。"""
+import pytest
+from rest_framework.test import APIClient
+
+pytestmark = pytest.mark.django_db
+
+
+@pytest.fixture
+def preview_token(home_page):
+    """为 home_page 生成一条预览快照记录，返回可用于查询接口的 token。"""
+    preview = home_page.create_page_preview()
+    preview.save()
+    return preview.token
+
+
+def test_page_preview_returns_draft_snapshot_for_valid_token(home_page, preview_token):
+    client = APIClient()
+    response = client.get(
+        "/api/v2/page_preview/",
+        {"content_type": "home.homepage", "token": preview_token},
+    )
+
+    assert response.status_code == 200
+    assert response.data["title"] == home_page.title
+
+
+def test_page_preview_returns_404_for_unknown_token(home_page):
+    client = APIClient()
+    response = client.get(
+        "/api/v2/page_preview/",
+        {"content_type": "home.homepage", "token": "does-not-exist"},
+    )
+
+    assert response.status_code == 404
+
+
+def test_page_preview_returns_404_for_mismatched_content_type(home_page, preview_token):
+    """token 是为 home.homepage 生成的，用错误的 content_type 查询应查不到记录。"""
+    client = APIClient()
+    response = client.get(
+        "/api/v2/page_preview/",
+        {"content_type": "blog.blogpage", "token": preview_token},
+    )
+
+    assert response.status_code == 404