v1.6.3.1 — Heatmap Dashboard

New Heatmap dashboard visualizing six metrics (Heart Rate, Steps, Stress,
Body Battery, SpO2, Respiration) as time-of-day × date grids.

While building it, two independent long-standing bugs surfaced and got
fixed along the way:

• SpO2 and Respiration intraday data was being silently dropped by the
  data broker for every dashboard, not just this new one — a structural
  mismatch between how Garmin's raw data is shaped and how it was being
  read. No data was ever lost (the raw archive was always correct), but
  none of it reached any dashboard.
• Respiration's quality assessment was checking a key name that doesn't
  exist, so it could never be labeled as fully present.

Also: the Mirror Import dialog no longer asks you to "confirm" a password
you're just unlocking, not creating.

Full detail in CHANGELOG.md.