Extract custom emoji from ActivityPub objects (Fedify Emoji tags) and
Mastodon API (status.emojis, account.emojis). Replace :shortcode:
patterns with <img> tags in the unified processing pipeline.
Emoji rendering applies to post content, author display names, boost
attribution, and quote embed authors. Uses the shared postProcessItems()
pipeline so both reader and explore views get emoji automatically.
Bump version to 2.5.1.
Confab-Link: http://localhost:8080/sessions/e9d666ac-3c90-4298-9e92-9ac9d142bc06
