feat: Support insulin concentrations (U-10 through U-500) in Trio

[Copilot]

Summary

Implements insulin concentration support for non-standard insulin strengths (U-10 through U-500) in Trio. This allows users of concentrated (U-200, U-500) or diluted (U-10, U-25, U-50) insulin to use their real clinical values for all therapy settings, while Trio automatically translates commands at the pump boundary.

Architecture: "Concentration Translator" Pattern

• Everything above the translator thinks in real insulin units (IU)
• Everything below (PumpManager/LoopKit) thinks in pump-native (volume-equivalent) units
• For U-100 (default), all translations are identity — zero behavioral change for existing users

User/Algorithm/Storage (real units)
        │
  ConcentrationService  ← translates at boundary
        │
  PumpManager (pump-native units, unchanged)

Concentration Factor

factor = concentration / 100
To pump:   pumpUnits = realUnits / factor
From pump: realUnits = pumpUnits × factor

Changes

New Files

File	Description
InsulinConcentration.swift	Enum model (U-10 through U-500) with factor computation
ConcentrationService.swift	Protocol and implementation for translating between real and pump units
ConcentrationServiceTests.swift	Comprehensive unit tests (25+ test cases)

Modified Files

File	Description
APSManager.swift	Wire outbound translation (enactBolus, enactTempBasal, performBolus, performBasal, roundBolus, fetchCurrentTempBasal)
PumpHistoryStorage.swift	Wire inbound translation (storePumpEvents for bolus and tempBasal)
DeviceDataManager.swift	Translate reservoir readings to real units
TrioSettings.swift	Update insulinConcentration from raw Decimal to InsulinConcentration enum with legacy migration
ServiceAssembly.swift	Register ConcentrationService in DI container
UnitsLimitsSettingsRootView.swift	Add concentration UI section with toggle, picker, and safety notice
UnitsLimitsSettingsStateModel.swift	Add concentration state bindings
SettingItems.swift	Add concentration search terms

Key Design Decisions

• Zero algorithm changes — determine-basal.js, IOB, COB, TDD all untouched
• Zero LoopKit/pump driver changes — works with all pumps without forking
• Safety limits preserved — maxIOB, maxBolus stay in real clinical units
• Backward compatible — defaults to U-100 (identity function = zero behavioral change)
• Gated behind toggle — allowDilution must be enabled before concentration can be changed
• Legacy migration — handles existing Decimal format for insulinConcentration gracefully

Testing

• 25+ unit tests covering all concentrations, round-trips, edge cases, Codable, and mock service
• Tests cover: U-10, U-25, U-50, U-100, U-200, U-300, U-500
• Verifies identity behavior for U-100 (no change from current behavior)
• Verifies outbound/inbound translation accuracy
• Verifies reservoir conversion

What's Untouched (by design)

• determine-basal.js — algorithm sees real units, no changes needed
• IOB/COB/TDD calculations — all operate on stored real units
• Nightscout/Tidepool uploads — already store real units from CoreData
• LoopKit pump drivers — no fork needed
• Bolus calculator — works in real units