[B3] Recaps and comparatives: yearly Rewind, monthly retro, anonymous percentiles

Backlog, explicitly late.

Ideas parked here

• Yearly Rewind. Your year in numbers, top rated, the genre that exploded, longest streak, plus a shareable image. High potential, but it demands real design work and, above all, accounts with several months of history — which does not exist yet. Premium candidate (see [B9]). Should be one of the last features, not one of the first.
• Monthly retrospective. Lighter version, pushed through the existing NotificationDigestService infrastructure. Lower enthusiasm, but it is the incremental path toward the Rewind.
• Anonymous percentiles — "you are in the top 10% of documentary watchers". All the satisfaction of comparison, none of the leaderboard's effects: no name, no race. Complements [G7] rather than duplicating it.

Existing groundwork

The stats/ module already computes most of the aggregates: video-temporal, rating-distribution, decade, cross-domain-totals.

Update (October 2026)

• Most of the aggregates now exist: the activity heatmap, minutes per month and per year, "on this day", social stats, and the year's XP (LeaderboardPeriod.year). The remaining work is mostly the staging and the shareable image.
• Open question on timing: a Rewind for December has to start now, which conflicts with "explicitly late" above. To be decided.
• Premium angle: the Rewind itself stays free; alternative styles for the shareable image could be premium (see [B9]).

Relevant code: stats/video-temporal.util.ts, ee/stats/social-stats.util.ts, stats/on-this-day.util.ts.