Feature request: Support Mastodon 4.6 Collections

[joebarbere]

Mastodon 4.6 (June 2026) introduced Collections: public/unlisted, shareable, curated lists of up to 25 accounts, shown on the curator's profile under a "Featured" tab. They're consent-based (members opt in via discovery settings, get notified, and can revoke), and have their own API (/api/v1/collections, plus accounts/:id/collections and accounts/:id/in_collections) and two new notification types (added_to_collection, collection_update). The official iOS app currently supports viewing them.

Ice Cubes has no Collections support today. Proposed phases:

1. Read-only viewing — show an account's collections on their profile and let users browse a collection's members. (PR incoming.)
2. Notifications — handle added_to_collection / collection_update types.
3. Management — create/edit/delete your own collections, add/remove members (with the 25-account cap and consent-error handling), revoke yourself from others' collections.

API notes from testing against mastodon.social (4.6): GET accounts/:id/collections wraps the array as {"collections": [...]}, and GET collections/:id returns {"collection": {...}, "accounts": [...]} with the member accounts already hydrated. On servers older than 4.6 the endpoints 404, so the feature can degrade by simply not rendering.