Update README.md - change Hugo version from latest to specific version

[stumbo]

The local build instructions have been updated to specify the version of Hugo. Initially they specified latest, this worked until breaking changes were introduced in Hugo v0.156.0. Running Hugo with this or later versions causes errors when running hugo server locally.

The breaking changes will be handled separately in Issue 2534.

The README file is now updated to use the same version of Hugo we are deploying to our website.

In addition, updated the GitHub action to compare the version of Hugo in the README and deployed by the GitHub action on a push or pull operation. Merges into main will fail if they have drifted apart. This will help ensure that when we roll the version of Hugo the documentation is correct.

Here's an example of what a failure will look like:

Run echo "Checking README.md for Hugo version $HUGO_VERSION"
Checking README.md for Hugo version 0.155.3
Error: README.md badge does not reference Hugo version 0.155.3
Error: README.md download URL does not reference Hugo version 0.155.3
Update README.md to use Hugo version 0.155.3
Error: Process completed with exit code 1.

[Copilot]

Pull request overview

Pins the Hugo version in README.md install instructions to 0.155.3 (matching the CI workflow) and adds a CI validation job to catch future version drift between the README and the workflow's HUGO_VERSION env var. Also adds pull_request trigger support and updates documentation to reflect the new workflow structure.

Changes:

• Replaced dynamic "latest" Hugo download commands in README with pinned version 0.155.3 URLs and cleaned up example output
• Added validate-docs CI job to verify README references match the configured Hugo version
• Added pull_request trigger to the workflow and skips deploy on PRs

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
README.md	Pins Hugo version in install instructions, updates example output, fixes config path and GCS engine ID, documents new workflow jobs
.github/workflows/gh-pages.yml	Adds pull_request trigger, validate-docs job, updated build conditions, skips deploy on PRs

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[pamoroso]

I'm not familiar with the internals of Hugo or YAML but I think it works as intended.

[masinter]

please respond to the copilot-generated review comments, if only to accept or reject the proposed hanges to the PR.

[stumbo]

I'm good with Copilot's suggestions and Paolo's merging them in. I'm going to go ahead and merge the PR.