Calculate - HRR after high-intensity workouts #516

It would be valuable for Noop to calculate Heart Rate Recovery (HRR) after sufficiently intense workouts. HRR should only be shown for workouts where the user reached a meaningful cardiovascular load, for example when heart rate entered at least Zone 3-4 or exceeded a configurable threshold such as 70% of max heart rate for a minimum duration.
After an eligible workout, Noop should calculate:
HRR after 1 minute
HRR after 2 minutes
HRR after 5 minutes
HRR is defined as the difference between peak heart rate at the end of the workout and the heart rate measured 1, 2, and 5 minutes later. The app should present the result as a simple recovery card, for example: “Peak HR 176 bpm, HRR-1 24 bpm, HRR-2 38 bpm, HRR-5 58 bpm.”
The feature should also include a trend graph showing HRR development over time, especially across the last 30 days, with optional views for 7 days and 90 days. The graph should make it easy to spot whether recovery is improving, stable, or declining. It would be especially useful to display separate lines for 1-minute, 2-minute, and 5-minute HRR.
Indicative reference ranges can be shown in the UI as guidance:
HRR after 1 minute> 25 bpm: excellent
18-25 bpm: good
12-17 bpm: below average
< 12 bpm: low

HRR after 2 minutes> 40 bpm: excellent
30-40 bpm: good
22-29 bpm: below average
< 22 bpm: low

HRR after 5 minutesno universal standard, but a clearly larger drop than at 2 minutes should be expected; trends over time are more useful than a hard cutoff