Heart v1.0.16 — Session analysis, battery banner, BLE fix

What's new

• Session analysis — every session in Trends now has a Detail button. Tap it to see an interactive HR trace with zone-boundary overlays, a stacked zone-time breakdown, a stats grid (avg / max / min HR, duration, load, active kcal), a GPS map for outdoor sessions, and next-night sleep context.
• Battery optimisation banner — on Android, a one-tap amber banner on the home screen alerts you when battery optimisation is blocking overnight recording. Tap "Fix it" to grant the exemption without digging through Settings.
• BLE scanning fix — a missing ProGuard keep rule for flutter_blue_plus caused device scanning to silently fail in release builds. Fixed.
• Duration display — sessions under 1 minute now show "< 1m" instead of "0m" in both the session list and the analysis screen.