refactor: extract shared resolve-pr-from-workflow-run action (#11336)

## Summary

Extract duplicated PR-number-resolution logic from
`workflow_run`-triggered workflows into a shared composite action at
`.github/actions/resolve-pr-from-workflow-run/`.

## Changes

- **What**: New composite action that resolves PR number from
`workflow_run` context using `pull_requests[0]` with
`listPullRequestsAssociatedWithCommit` fallback. Updated 4 consumer
workflows; removed dead artifact-stored PR metadata from 2 CI workflows.
- **Files touched**:
  - `.github/actions/resolve-pr-from-workflow-run/action.yaml` (new)
- `.github/workflows/pr-vercel-website-preview.yaml` (uses shared
action)
- `.github/workflows/pr-report.yaml` (uses shared action with
`check-staleness: true`)
- `.github/workflows/ci-tests-storybook-forks.yaml` (replaced
`pulls.list` scan)
- `.github/workflows/ci-tests-e2e-forks.yaml` (replaced `pulls.list`
scan)
- `.github/workflows/ci-size-data.yaml` (removed dead
`number.txt`/`base.txt`/`head-sha.txt` writes)
- `.github/workflows/ci-perf-report.yaml` (removed dead `perf-meta`
artifact)

## Review Focus

- The fork workflows previously used `pulls.list` (fetches all open PRs,
linear scan by SHA). The shared action uses the more targeted
`workflow_run.pull_requests[0]` + `listPullRequestsAssociatedWithCommit`
fallback.
- `coverage-slack-notify.yaml` was intentionally left unchanged — it
parses merged commit messages on `main` pushes, which is a different use
case.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-11336-refactor-extract-shared-resolve-pr-from-workflow-run-action-3456d73d365081e5b8f5ea29c020763e)
by [Unito](https://www.unito.io)

---------

Co-authored-by: bymyself <cbyrne@comfy.org>
Co-authored-by: Amp <amp@ampcode.com>

.github/workflows/ci-size-data.yaml

@@ -32,13 +32,6 @@ jobs:
       - name: Collect size data
         run: node scripts/size-collect.js
 
-      - name: Save PR metadata
-        if: ${{ github.event_name == 'pull_request' }}
-        run: |
-          echo ${{ github.event.number }} > ./temp/size/number.txt
-          echo ${{ github.base_ref }} > ./temp/size/base.txt
-          echo ${{ github.event.pull_request.head.sha }} > ./temp/size/head-sha.txt
-
       - name: Upload size data
         uses: actions/upload-artifact@v6
         with: