fix(403): Make design consistent with 404 + add default hint

[joshtrichards]

• Resolves: "Access forbidden" (HTTP 403) page displayed as dead end #39584

Summary

• Adds a default hint message (consistent with 404)
• Adds an icon (consistent with 404 handler)
• Adds box around main content (consistent with 404 handler)
• Fixes an HTML syntax bug that was causing the footer to appear immediately after the error

After:

And, for comparison, the 404 page already looks like this:

Before:

TODO

• ...

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[susnux]

Look good