Estimate daily calories on-device when the wearable reports none

[saksham2001]

Summary

Rings that don't report calories (TK18/LuckRing) — and history syncs on rings that do (Colmi sends calories only in live packets) — left days showing "—". This adds an on-device daily estimate: Mifflin-St Jeor BMR accrued over elapsed minutes + net active energy from workouts (existing Keytel/MET engine), all-day HR (Keytel gated at 60% HRmax so resting HR spikes never count), and cadence-tiered step energy from history buckets. Each interval is attributed to exactly one estimator, so nothing double-counts.

A device-reported value always wins at read time (ActivityDaily.effectiveCalories), so this only fills days with no device calories; extending to all wearables later is a one-line gate change. The calorie goal ring keeps measuring the active-energy portion vs the 500 kcal goal; the displayed number is the total.

Recompute hooks: history-bucket sync (batched, flushed at sync done), live packets from no-calorie devices (throttled), workout finish/edit/delete, late HR backfill, profile changes, launch backfill. New estimatedActiveCalories field on ActivityDaily is an additive lightweight migration.

Type of change

• ✨ New feature (non-breaking change that adds functionality)

How was this tested?

• Added / updated unit tests (PulseLoopTests) — 17 new tests in DailyCalorieEstimatorTests (formula values, FLEX gating, overlap exclusion, midnight proration, device-wins selection, re-sync idempotency)
• Ran the test suite locally — full suite green
• Tested with demo data (-seedDemo YES, no hardware) — new -demoEstimatedCalories YES launch arg reshapes seeded days into ring-history days; Today/Activity show the estimated total instead of "—"

Privacy & data

• This change does not send health data off-device without explicit user action.
• No secrets, API keys, or personal data are committed.

Checklist

• My code follows the project's style (SwiftLint passes).
• I ran the tests and they pass.