chore(ci): delete dead preview workflow, relax coverage and Slack requirements

[rekmarks]

Cleanups around the preview-build workflow, which turns out never to have been able to
run, plus two constraints that were stricter than the tooling underneath them.

Changes

• Delete publish-preview.yml. This is a feature used by MetaMask/core that we never implemented. The workflow invoked yarn prepare-preview-builds,
  yarn publish-previews, and scripts/generate-preview-build-message.ts. None of these
  exist, and git log shows the latter two never did, so any @metamaskbot publish-preview
  comment would have failed on the first step. PUBLISH_PREVIEW_NPM_TOKEN was never
  configured either.

• Drop the orphaned publish:preview scripts and their constraint. That workflow was
  the only consumer, so all 31 copies of the script are unreachable, as is the
  yarn.config.cjs constraint requiring one of every published package. Removing it from
  template-package also stops new packages from inheriting it.

• publish-release.yml: SLACK_WEBHOOK_URL is now required: false. The
  slack-webhook-url input of MetaMask/action-npm-publish is itself optional, and all
  four of its Slack steps are guarded on the value being non-empty. The publish-npm job
  in this same file already omits the input, so that path is already exercised.

• coverage-report.yml: derive the Pages URL, and tolerate a missing baseline. The URL
  now comes from github.repository_owner and github.repository instead of being
  hardcoded. A failed baseline fetch emits a warning and an empty compare path instead of
  exit 1, so the report renders without trend indicators rather than painting the check
  red.

Testing

yarn constraints, yarn lint:eslint, and yarn lint:dependencies pass, as do
actionlint, shellcheck, and prettier --check. No source changed, so build and test
are unaffected — though constraints and depcheck between them parse every package.json
touched here.

The coverage change is the only one with logic worth exercising. json-summary-compare-path
has no default in the action's action.yml and is read via core.getInput behind a
truthiness check, so an empty string is identical to omitting the input. The
if curl ...; then ... else ... fi form is exempt from errexit, so a 404 takes the else
branch rather than aborting the step — confirmed against a real 404 under bash -e.

coverage-report is not in the all-jobs-complete gate, so this changes only whether that
check reports green, not mergeability.

🤖 Generated with Claude Code

---

Note

Low Risk
Changes are limited to CI workflows and package scripts; release publish logic is unchanged except optional Slack secret validation.

Overview
This PR trims CI and monorepo constraints around preview publishing and tightens coverage reporting behavior.

Coverage reporting now builds the GitHub Pages baseline URL from github.repository_owner and github.repository instead of a hardcoded host. If that fetch fails, the workflow logs a warning, leaves the compare path empty, and still posts the PR coverage report without trend deltas instead of failing the job.

Release workflow treats SLACK_WEBHOOK_URL as optional on the reusable publish-release workflow, matching optional Slack handling in the publish action.

Preview publishing is removed end-to-end: the publish-preview.yml workflow is deleted, every workspace loses the publish:preview script, and yarn.config.cjs no longer requires that script on published packages.

^{Reviewed by Cursor Bugbot for commit acc8f04. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	73.05% 🟰 ±0%	9790 / 13401
🔵	Statements	72.9% 🟰 ±0%	9954 / 13653
🔵	Functions	73.6% 🟰 ±0%	2301 / 3126
🔵	Branches	67.27% 🟰 ±0%	4023 / 5980

File Coverage

No changed files found.

Generated in workflow #4710 for commit acc8f04 by the Vitest Coverage Report Action