feat: add Workers Previews support

[yomna-shousha]

What

Adds support for wrangler preview in wrangler-action. Preview commands now parse Wrangler Preview artifacts, expose Preview-specific outputs, and can create GitHub Deployments and job summaries when gitHubToken is provided.

The README documents the direct Wrangler workflow first, so users can copy plain GitHub Actions YAML without taking a dependency on this action. It then shows the wrangler-action wrapper for users who want action outputs, GitHub Deployments, and job summaries.

Changes

• Adds a Zod schema for Wrangler Preview artifacts.
• Parses preview command output and sets Preview outputs.
• Adds fallback stdout parsing for Preview commands.
• Creates non-production GitHub Deployments for Previews when gitHubToken is provided.
• Renders a Workers Preview job summary.
• Extends --var auto-injection to preview commands.
• Adds README guidance for plain npx wrangler preview --json, wrangler-action, and deeper automation examples.
• Adds a minor changeset so this ships in the next wrangler-action v4 release.

Outputs

Output	Description
deployment-url	Stable Preview URL, kept compatible with existing deployment URL usage
preview-url	Stable Preview URL for the branch or Preview name
preview-deployment-url	Immutable URL for the specific Preview deployment
preview-name	Preview name
preview-id	Preview resource ID
preview-deployment-id	Deployment ID within the Preview

Example

Users can run Wrangler directly:

name: Preview

on: [pull_request]

jobs:
  preview:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v6
      - run: npx wrangler preview --json
        env:
          CLOUDFLARE_API_TOKEN: ${{ secrets.CLOUDFLARE_API_TOKEN }}
          CLOUDFLARE_ACCOUNT_ID: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}

Or use wrangler-action when they want Preview outputs, GitHub Deployments, and the job summary:

- uses: actions/checkout@v6
- id: preview
  uses: cloudflare/wrangler-action@v4
  with:
    apiToken: ${{ secrets.CLOUDFLARE_API_TOKEN }}
    accountId: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}
    command: preview
    gitHubToken: ${{ secrets.GITHUB_TOKEN }}

Verification

Local verification passes:

• npm run build
• npm test -- --run
• npm run check

The wrangler_action_self_testing PR check currently fails at a live deployment fixture because this PR run does not have access to the Cloudflare secrets required by that workflow. The build, unit tests, and formatting steps in that same check pass before the secrets-backed fixture runs.

[WillTaylorDev]

Failing CI check, but doesn't look related to your changes