feat: add TL;DR block to DBLab 4.1 post and restore preview envs

[NikolayS]

Summary

Two requests in one branch:

1. AI TL;DR block on the DBLab 4.1 post

blog/20260408-dblab-engine-4-1-released.md now uses the same <TldrTabs>
component (Founders / Developers / DBAs / Managers / Ask AI) that the
invalid-index post uses. The article body itself is fleshed out from the live
page so the post no longer relies on out-of-repo content.

The Ask AI tab is wired up with a focused aiContext summary of the release
so the chat can answer 4.1-specific questions without leaking unrelated context.

2. Preview environments — diagnosis and fix

Why they disappeared. .gitlab-ci.yml had a single build_and_push_staging
job set to except: master. Every non-master push deployed to the same
NAMESPACE: staging with the same DOCS_NAME: docs — so each branch just
overwrote the previous one. There were no per-branch environments. The unused
deploy/configs/review.sh (just export REPLICAS=1) was a leftover from when
this used to be a real review-apps setup.

Fix.

• New build_and_push_review / deploy_review jobs for every non-master /
  non-staging branch. They deploy into the review namespace as
  docs-$CI_COMMIT_REF_SLUG, with the GitLab environment named
  review/$CI_COMMIT_REF_SLUG and the URL
  https://$CI_COMMIT_REF_SLUG.$PREVIEW_BASE_DOMAIN
  (override PREVIEW_BASE_DOMAIN as a CI variable if your infra uses a
  different host).
• New stop_review job wired via environment.on_stop so the per-branch
  Deployment + Service are torn down when the branch is deleted. auto_stop_in: 1 week is a backstop for orphaned envs.
• build_and_push_staging / deploy_staging are now scoped to the staging
  branch only — the static staging env at v2.postgres.ai is unchanged but
  feature branches no longer trample it.
• deploy/configs/review.sh now sets URL, BASE_URL, and the staging-backend
  endpoints so the preview build actually has a working frontend config.

3. GitLab ↔ GitHub mirror model documented in CLAUDE.md

Reflects the actual setup: master flows GitLab → GitHub; development branches
flow GitHub → GitLab via .github/workflows/mirror-to-gitlab.yml. Practical
implication: Claude Code (GitHub-integrated) starts work here, the branch
auto-mirrors to GitLab, and the MR / merge happens there. master only updates
on GitHub via the mirror after a GitLab merge.

Test plan

• CI on this branch produces a build_and_push_review job and a
  deploy_review job (not a build_and_push_staging).
• deploy_review deploys docs-claude-add-tldr-fix-previews-xpq4v into
  the review namespace.
• GitLab Environments page shows review/claude-add-tldr-fix-previews-xpq4v
  with a Stop button.
• Visit the preview URL and confirm the new DBLab 4.1 post renders with the
  TL;DR tabs (including the Ask AI tab connecting to the WS backend).
• Delete the branch and confirm stop_review runs and removes the
  Deployment + Service.
• master build/deploy paths are unchanged.

https://claude.ai/code/session_015AC273dXNKXd8gG5QpC152

---

Generated by Claude Code