feat(medications): add per-schedule units-per-dose column

Add a nullable units_per_dose to medication_schedules so a split-dose
plan can consume a different unit count at different times of day (a
whole tablet in the morning, a half at noon) on ONE medication instead
of two. NULL inherits the medication-level units_per_dose, so every
existing row keeps its current behaviour. Migration 0332 adds one
nullable Decimal(10,4) column with no backfill.

prisma/migrations/0332_schedule_units_per_dose/migration.sql

@@ -0,0 +1,6 @@
+-- #219 — per-schedule inventory units consumed per dose.
+-- Additive, nullable, no backfill: every existing schedule row reads NULL and
+-- the consume hook keeps inheriting the medication-level `units_per_dose`, so
+-- behaviour is unchanged until a user sets a per-slot value. Same
+-- Decimal(10,4) grain as `medications.units_per_dose`.
+ALTER TABLE "medication_schedules" ADD COLUMN "units_per_dose" DECIMAL(10,4);

prisma/schema.prisma

@@ -2738,6 +2738,16 @@ model MedicationSchedule {
   windowEnd            String                 @map("window_end") // HH:mm format, e.g. "10:00"
   label                String? // e.g. "Morning", "Evening"
   dose                 String? // Per-schedule dose override; null = use Medication.dose
+  /// v1.37.10 (#219) — per-schedule inventory units consumed per dose. The
+  /// intake consumption hook counts UNITS (tablets, ampoules, puffs); a
+  /// split-dose plan takes a different unit count at different times of day
+  /// (a whole tablet in the morning, a half at noon). NULL inherits the
+  /// medication-level `Medication.unitsPerDose`, so every existing row keeps
+  /// its current behaviour. Same Decimal(10,4) grain + curated fraction /
+  /// whole-number posture as the medication-level column; the consume hook
+  /// matches a taken intake's slot to its schedule by wall-clock time and
+  /// reads this first, falling back to the medication level on NULL.
+  unitsPerDose         Decimal?               @map("units_per_dose") @db.Decimal(10, 4)
   /// Legacy string encoding of the cadence ("null | 1,3,5 | i2;1,3,5").
   /// v1.5 writes go to `rrule` / `rollingIntervalDays` and v1.5.1 flipped
   /// the readers to consult the new fields first.