Consider a user-friendly 'streak'

Some users like to use third-party add-ons to track their 'streak' to provide motivation/keep them honest. I've resisted adding such a feature up until now, because the existing implementations can be toxic - users get overly disappointed when they miss a day for some reason, and feel inclined to do things like set the date back in time and/or do single-card reviews to maintain their streak.

I think a better approach would be something that averages performance out over time, and allows for low/off days. Preferably where the user decides the bar they want to set, perhaps guided by their daily workload amount. And maybe a rolling average, so that bad past performance doesn't lead to users getting stuck in a hole?

No files, tests, or entry points are named. Start by clarifying the desired streak metric, configurable bar, and rolling-average behavior before locating the relevant application code. Done would mean an agreed design and an implemented, tested user-facing feature.

Written by the indexing model from the issue text.