Workout auto-detection is over-sensitive (triggers on a short walk) with no user-facing disable toggle

[abdulsaheel]

Reported in #102's feedback dump, not yet split into its own issue.

Last time I tried auto workout detection it was showing very short workouts of like 16mins? I was very confused about this. (Also a tad to sensitive, I got it triggered by just walking a bit lol). Consider an option to disable autodetection.

Confirmed: there is currently no user-facing setting anywhere in lib/ui/profile/ or AppState to disable auto-detected workout suggestions (grep'd for autoDetect/disableAutoDetect-style prefs — no hits).

Two asks bundled here:

1. Tune sensitivity — a short/light walk shouldn't cross the auto-detect threshold as its own "workout." Worth revisiting autoDetectWorkouts in the analytics workout family against a higher intensity/duration floor.
2. Add an opt-out — a settings toggle to disable auto-detected workout suggestions entirely for users who find them noisy, independent of tuning .

Same feedback thread separately suggested (not filing separately, lower priority, note for whoever picks this up): confirming an auto-detected workout would ideally show the HR graph + detected time range so the user can adjust the boundaries before logging it, rather than a blind accept/dismiss.