Thunder follow-up fix pass

What was corrected in this pass:
- Reduced the divider/banner image height so the new divider no longer appears oversized or cropped too tall.
- Kept the provided new divider asset, but changed the shared CSS to tile it cleanly across the width.
- Audited admin/public delete + clear flows that were still using hardcoded /admin/ paths.
- Normalized key admin action links to relative paths so they work on local/test installs and nested setups.
- Fixed public contact form schema so it matches admin contact message parsing.
- Fixed public contact recent-message display to read the same block format admin reads.
- Kept a legacy contact file write for compatibility with older tools still expecting contact.txt.

Files updated in this pass:
- assets/css/style.css
- contact.php
- send_contact.php
- admin/contact.php
- admin/djs.php
- admin/fans.php
- admin/friends.php
- admin/navigation.php
- admin/backup.php
- admin/chat.php
- admin/events.php
- admin/media.php
- admin/pages.php
- admin/radiostats.php
- admin/schedule.php
- admin/newsreel_admin.php

Main focus of this pass:
- divider image sizing
- contact message submit/read consistency
- admin delete/clear/edit links using paths that actually resolve in test/local environments
