Fix zpages CSS and JS CDN URLs

[pradhyum6144]

Fixes #8470

Problem
The zpages module references Material Design Lite CSS and JavaScript from code.getmdl.io, which is currently returning 403 Forbidden errors, breaking the zpages UI.

Solution
Replaced the broken CDN with cdnjs.cloudflare.com, which is actively maintained and accessible.

Changes

• Updated zpages/internal/templates/header.html to use cdnjs.cloudflare.com CDN URLs
• Both CSS and JS URLs have been verified to return HTTP 200
• Added CHANGELOG entry under "Fixed" section

Testing

• Verified new CDN URLs are accessible (HTTP 200)
• All zpages tests pass: go test -race ./zpages/...
• No functional changes to the code, only CDN URLs updated

Verification

$ curl -I https://cdnjs.cloudflare.com/ajax/libs/material-design-lite/1.3.0/material.indigo-pink.min.css
HTTP/2 200

$ curl -I https://cdnjs.cloudflare.com/ajax/libs/material-design-lite/1.3.0/material.min.js
HTTP/2 200

[pradhyum6144]

Hello @dashpole sir, can review this if there is any changes need mention i will change or please review and merge it .
Thank you sir.

[dashpole]

Thanks!

[pradhyum6144]

Thanks!

Thank you sir for assigning this issue can you please merge it. If there are any issues please assign me i am ready to work.

[dashpole]

This requires a second review.

[MrAlias]

LGTM outside of the changelog entry needed fix.

[MrAlias]

@pradhyum6144 the only requirement this PR still needs to satisfy is to remain open for a full day. Thanks for the contribution.