chore: remove the Playground preview workflows

[josephfusco]

Deletes playground-preview.yml, playground-preview-publish.yml, and playground-preview-cleanup.yml.

Why

Playground Preview Publish has failed on all 8 of its runs, three of them today. Because it runs on workflow_run, its failures never show in gh pr checks and never gate a PR — so it sat broken unnoticed.

I traced the causes to 52c0077, the commit that first added these workflows. There was never a working version to regress from; they went in broken.

The breakage is structural, not a typo:

1. test -f artifacts/release-assets/ tests a directory, always false under bash -e. Kills the job ~10s in, before anything else runs.
2. Two of three release assets were never real. A "seeder" and a "helper" were scaffolded as bare paths (artifacts/release-assets/) with filenames never filled in — and no such files exist in the repo. playground-preview.yml:69 stages only sync-storage.zip.
3. blueprint-40.json doesn't exist. It's transformed on line 141 and advertised in the sticky comment as a "40 demo users" variant.
4. blueprint.json has no writeFile steps, so the seeder/helper half of the jq transform is a no-op regardless. Its two endswith("/") branches (132–133) are byte-identical, making the elif unreachable.

The sticky comment also advertised "seeds 5 demo users," which blueprint.json never did — it creates the wp_collaboration table and activates plugins.

Safety

• No Playground job is a required status check (required: gate, phpcs, phpstan, phpunit ×2, typos, plugin-check)
• Nothing outside the three files references them
• No preview-pr-* releases or tags were ever produced — consistent with publish never succeeding
• actionlint clean on the remaining workflows

blueprint.json is kept. The README badge points Playground at it directly via raw.githubusercontent.com and never involved these workflows.

If per-PR previews are wanted later, they're better rebuilt than repaired.

Use of AI Tools

Assisting with the audit and removal.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.90%. Comparing base (3401ef3) to head (991c664).

Additional details and impacted files

@@            Coverage Diff            @@
##               main      #38   +/-   ##
=========================================
  Coverage     63.90%   63.90%           
  Complexity       35       35           
=========================================
  Files             7        7           
  Lines           266      266           
=========================================
  Hits            170      170           
  Misses           96       96           

Flag	Coverage Δ
multisite	63.90% <ø> (ø)
phpunit	64.63% <ø> (ø)

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