fix: add versioning to cached pdf

[JohnGuilding]

This PR:

• Adds versioning to the state of private voting url
• Restores caching behaviour

The mozilla docs recommend the following for immutable resources (scroll down to immutable section):

A modern best practice for static resources is to include version/hashes in their URLs, while never modifying the resources — but instead, when necessary, updating the resources with newer versions that have new version-numbers/hashes, so that their URLs are different. That's called the cache-busting pattern.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Review	Updated (UTC)
website-v2-production	Ready	Preview, Comment	Dec 17, 2025 2:45pm

[vercel]

@JohnGuilding is attempting to deploy a commit to the Andy's projects Team on Vercel.

A member of the Team first needs to authorize it.