WPMediaVerse 2.2.1 - messaging, dark mode, and BuddyBoss compatibility fixes

Maintenance release clearing all open QA cards for messaging, dark mode, and BuddyBoss compatibility.

• Fix - Fatal error on activity feeds containing media imported from BuddyBoss. The feed crashed instead of rendering when an activity stored its attachment ids as a list.
• Fix - Chat messages sometimes did not arrive until the member reloaded or switched threads. A message sent in the same second as the live-update cursor was skipped, and the chat never asked for it again.
• Fix - Chat reactions on an already-delivered message sometimes never appeared for the other member until they reloaded the page. A reaction added in the same second as the live-update cursor was skipped, which lost roughly one reaction in five.
• Fix - Deleting a conversation and messaging the same member again no longer leaves the other member with two chat threads. Delete now clears your copy of the history and the pair keeps a single conversation.
• Fix - The conversation list shows a Photo, Video, or Audio placeholder when the newest message is a media attachment with no text, instead of a blank line.
• Fix - Media action buttons on BuddyPress profile tabs and the My Media dashboard (Upload Media, Create Album, Edit Media, collections) are readable in dark mode with visible hover states.
• Fix - Opening an album and clicking Share no longer shows a link icon next to the share icon.
• Fix - The chat composer's attachment chip stayed light grey in dark mode.
• Dev - Database migration v24 adds a per-user clear watermark (cleared_up_to) to conversation participants.
• Compat - Aligned with WPMediaVerse Pro 2.2.1. Install both updates together.