ECG recordings had no pill in the tab strip, no entry in the sub-page
manager, and no routed page — the only inbound pointer was a cross-link
card on the spot-pulse page. Hiding the overview ECG teaser left no route
back to a user's recordings.
- Add a routed `/insights/ecg` sub-page that reuses the existing ECG
section (heading suppressed so the page shell owns the title); the
overview teaser stays.
- Add an ECG entry to the Heart group of the tab strip, gated on a
dedicated `hasEcgRecordings` signal since ECG carries no measurement
type. The Heart group surfaces for an ECG-only device too. No ECG pill
appears without recordings.
- Mount the ECG cross-link on the resting-pulse and HRV pages, matching
its placement on the pulse page.
- List ECG in the sub-page manager under Heart, its eye toggling the ECG
overview section so hiding it is reversible.
- Point the metric catalog's ECG row at the new page.
- Add `navEcg`, the sub-page description, and the empty-state copy across
all locales.