Added Functionalities / Bug Fixes

[farrrunnner]

September/October 2026:

1. Finalised functionalities for heart rate drift/aerobic decoupling metrics (derived from the work of Johnston et al).

2. Fixed bugs:

• Made workout metrics use consistent segment boundaries and explicit segment labels.
• Updated Pace–HR decoupling and HR drift for selections, with clear unavailable states.
• Fixed pause handling, missing-sample calculations, and HR-zone double counting.
• Prevented stale values during zooming, resets, activity switches, and rescans.
• Fixed analytics cache invalidation, stale heatmaps, and today’s missing dashboard totals.
• Added regression coverage and Rust tests to CI. Typecheck, 23 frontend tests, 35 Rust tests, and production build passed.