Clean up current-run E2E dev stores

[alfonso-noriega]

WHY are these changes introduced?

After E2E shards finish, CI currently runs a current-run app cleanup job, but dev stores are only cleaned by each test's best-effort teardown. If a teardown is interrupted or flakes, stores can remain behind.

WHAT is this pull request doing?

Adds current-run dev store cleanup to the post-E2E cleanup job, before app cleanup, using the run token added in the parent PR. Store cleanup now also reuses the primed Playwright browser storage state, matching app cleanup and avoiding an extra Shopify Accounts login when possible.

The cleanup job now checks out github.sha from the base repository instead of ephemeral PR/merge-queue head refs, so cleanup is less likely to fail before running when temporary refs disappear.

How to test your changes?

• cd packages/e2e && pnpm tsc --noEmit
• cd packages/e2e && pnpm eslint "setup/**/*.ts" "helpers/**/*.ts" "tests/**/*.ts" "*.ts"
• node bin/run-knip-ci.js

Note: ESLint completed successfully with existing Nx project graph cache warnings for @nx/enforce-module-boundaries. The PR E2E cleanup job will exercise the workflow path in CI.

Post-release steps

None.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is not user-facing; no changeset is needed.