Apple Health sync with per-type toggles, workout export, and profile import - #80

Summary

Apple Health (HealthKit) integration, building on @hoveeman's #16 (thank you!) ported onto current main with user-facing customization: a master sync toggle (default off), per-data-type toggles (HR, SpO₂, HRV, temperature, sleep, steps/activity), a dedicated workout-export toggle (with GPS routes), and an ask-on-first-enable choice between full-history backfill and new-data-only.

Key differences vs #16: idempotent writes via HKMetadataKeySyncIdentifier/SyncVersion upsert (no delete-then-rewrite), one debounced HealthSyncPublisher instead of per-call-site sync triggers, watermark-based export tracking (no schema changes — syncedAt keeps its ring-freshness meaning), and read side limited to a profile import button (age/sex/height/weight, read-only authorization). Also adds a "Use advanced calories" toggle for the existing Keytel/MET estimator. Includes a "Remove PulseLoop data from Apple Health" action.

Deferred follow-ups: blood-pressure export (needs HKCorrelation), workout import, iOS 18 effort scores.

Related issues

Supersedes #16.

Type of change

• ✨ New feature (non-breaking change that adds functionality)
• 🎨 UI / DesignSystem change

How was this tested?

• Added / updated unit tests (PulseLoopTests) — 27 new tests (mappings, plausibility bounds, sync-ID determinism, prefs tolerant decode, watermark reset, calorie gate)
• Ran the test suite locally (⌘U in Xcode) — all 64 suites pass; SwiftLint clean
• Manual Health-app QA on simulator/device still pending (auth flows, duplicate-free re-export, Move-ring netting)

Privacy & data

• This change does not send health data off-device without explicit user action — everything is gated behind an opt-in master toggle (default off) plus per-type toggles; HealthKit stays on-device.
• No secrets, API keys, or personal data are committed.

Note for release: App Review Guideline 5.1.3 requires a privacy policy for HealthKit apps.

Checklist

• My code follows the project's style (SwiftLint passes).
• I ran the tests and they pass.
• I updated docs / README where relevant.
• I read the Contributing guide.