Rename plugin names in README to use bbb-plugin- prefix

[Copilot]

Summary

Updated all plugin names in the README table to consistently use the bbb-plugin- prefix, matching the recently renamed repositories.

Changes

• Renamed 11 plugin names in the Plugin Name column from plugin-X to bbb-plugin-X:
  • plugin-generic-link-share → bbb-plugin-generic-link-share
  • plugin-session-share → bbb-plugin-session-share
  • plugin-pick-random-user → bbb-plugin-pick-random-user
  • plugin-typed-captions → bbb-plugin-typed-captions
  • plugin-tour → bbb-plugin-tour
  • plugin-live-transcription → bbb-plugin-live-transcription
  • plugin-decrease-volume-on-speak → bbb-plugin-decrease-volume-on-speak
  • plugin-h5p → bbb-plugin-h5p
  • plugin-code-highlight → bbb-plugin-code-highlight
  • plugin-chat-mention → bbb-plugin-chat-mention
  • plugin-media-popout → bbb-plugin-media-popout
• Aligned table column widths for consistency across all rows (including bbb-plugin-picture-in-picture, bbb-plugin-pin-message, and bbb-plugin-reaction-stack which already had the correct prefix)

Notes

• The Sample Manifest URLs were intentionally left unchanged since they reference hosted paths (not repository names).
• Repository links were already updated in a prior commit.