implement visual tags for experimental settings

experimental features now marked with visual badges instead of text labels. <!-- This is an auto-generated comment: release notes by coderabbit.ai --> ## Summary by CodeRabbit * **New Features** * Settings items now show a visual "Experimental" badge. * Voice attachment recording, custom formatting popup, reaction bar position, chat views list, and the Non‑island UI option display the experimental badge. * Experimental label text consolidated into a single localized string for consistent display. <!-- end of auto-generated comment: release notes by coderabbit.ai -->