Prepare iOS health release requirements

[peter9teufel]

Proposed Changes

Summary

• update the iOS HealthKit usage description to match the imported Apple Health data
• move the iOS PowerSync database into an app-specific Application Support subdirectory
• exclude the iOS PowerSync database directory from backups
• migrate legacy iOS PowerSync database files into the new directory
• add regression coverage for the iOS health release-prep changes

Verification

• flutter test test/features/health/health_manifest_test.dart test/features/health/health_ios_release_prep_test.dart
• debug run on a physical iOS device succeeded
• verified the legacy DB migration path
• verified the backup exclusion method channel succeeds on-device

Why

• Apple Health import adds health-related local data on iOS, so the local PowerSync SQLite store should not remain in a backup-eligible location.
• The HealthKit usage description now reflects the actual read scope used by the app, including activity and sleep-related imports in addition to body measurements.
• Existing iOS installs may already have a PowerSync DB in the legacy location, so the migration preserves local data across the update while moving the database into an excludable subdirectory.

Related Issue(s)

Not applicable

Please check that the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Set a 100-character limit to avoid white space diffs (run dart format .)