Style audio and image cache browser

[RANGROO]

What changed

• adds a themed Audio & Image Cache browser matching the compact Dialectic layout
• lists recent cached audio with metadata and inline playback controls
• shows cached gallery files when Stobe has a data/pictures/gallery directory, with a safe empty state otherwise
• routes the Control Panel cache tab to the new browser instead of the raw directory listing

Why

Stobe's cache tab still exposed the unstyled Apache directory view while Dialectic had a proper integrated cache UI.

Validation

• php -l ui/cache_browser.php
• php -l ui/controlpanel_hub.php
• local endpoint returned HTTP 200 with no PHP warnings
• browser verified the active cache tab, Stobe theme, audio entries, and empty image state