Add Shiplight integration guide for Depot CI

[lucas-shiplight]

Summary

This draft adds a Shiplight integration guide under content/ci/integrations/.

The guide covers:

• configuring SHIPLIGHT_API_TOKEN in Depot CI Secrets
• running Shiplight browser tests on Depot compute
• installing the required Playwright browser
• uploading test results, screenshots, videos, and traces to Shiplight Cloud
• preserving report uploads when tests fail
• troubleshooting common secret and browser configuration issues

Validation

The workflow was validated end to end using:

https://github.com/lucas-shiplight/ci-test

The validation confirmed that:

• a GitHub push automatically triggers Depot CI
• Shiplight tests run successfully on a Depot CI runner
• the Depot CI secret is available to the test and report steps
• test results and artifacts are uploaded to Shiplight Cloud

Feedback requested

This PR is intended as a proposal for discussion. We would appreciate feedback on:

• whether Depot would like to include a Shiplight integration guide
• whether content/ci/integrations/ is the preferred location
• any workflow or wording changes the Depot team would recommend

We are happy to revise the content and placement based on the maintainers' feedback.