feat(schema): MeasurementType enum additions for Withings full coverage

Seven new enum values for v1.4.25 W5d. Source: Withings developer
guide — Data API → All Available Health Data — cross-referenced
against `.planning/research/withings-api-coverage.md` §3.

  - FAT_FREE_MASS (meastype 5) — Body+, Body Cardio, Body Comp, Body Scan
  - FAT_MASS (meastype 8) — same devices; mass form of BODY_FAT
  - MUSCLE_MASS (meastype 76) — Body+ family
  - SKIN_TEMPERATURE (meastype 73) — ScanWatch dermal reading. DISTINCT
    from BODY_TEMPERATURE: surface temps run ~32 °C, core ~37 °C, so
    they cannot share a bucket without corrupting analytics.
  - PULSE_WAVE_VELOCITY (meastype 91) — Body Cardio / Body Scan;
    indicator of arterial stiffness
  - VASCULAR_AGE (meastype 155) — Body Scan; composite of PWV + age
  - VISCERAL_FAT (meastype 170) — Body Comp / Body Scan; Withings'
    1–12 rating scale (not a percent)

Migration 0049 is additive only — every value is unconditional, no
backfill needed. The Withings client picks these values up once the
meastype → enum mapping lands (separate commit in this phase).

Unit map + plausibility ranges updated in `src/lib/validations/
measurement.ts` so the create-measurement validator accepts the new
types end-to-end.

prisma/migrations/0049_withings_full_metrics/migration.sql

@@ -0,0 +1,25 @@
+-- v1.4.25 W5d — Withings full coverage. Adds seven new
+-- MeasurementType enum values so the Withings ingest path can land
+-- body composition (Body+, Body Cardio, Body Comp, Body Scan),
+-- skin temperature (ScanWatch dermal reading — DISTINCT from core
+-- body temperature; sharing the bucket would corrupt analytics
+-- because surface temps run ~32 °C and core ~37 °C), pulse-wave
+-- velocity + vascular age (Body Cardio / Body Scan exclusives), and
+-- visceral fat (Body Comp / Body Scan rating).
+--
+-- See `.planning/research/withings-api-coverage.md` §3 for the gap
+-- scoring + the rationale of which meastypes ship in v1.4.25 vs
+-- defer to v1.5.
+--
+-- Additive only, forward-only — every new enum value is unconditional
+-- and no existing row needs to be backfilled. The Withings client
+-- starts emitting these values once `src/lib/withings/client.ts`
+-- gains the meastype → enum mapping (separate commit).
+
+ALTER TYPE "measurement_type" ADD VALUE IF NOT EXISTS 'FAT_FREE_MASS';
+ALTER TYPE "measurement_type" ADD VALUE IF NOT EXISTS 'FAT_MASS';
+ALTER TYPE "measurement_type" ADD VALUE IF NOT EXISTS 'MUSCLE_MASS';
+ALTER TYPE "measurement_type" ADD VALUE IF NOT EXISTS 'SKIN_TEMPERATURE';
+ALTER TYPE "measurement_type" ADD VALUE IF NOT EXISTS 'PULSE_WAVE_VELOCITY';
+ALTER TYPE "measurement_type" ADD VALUE IF NOT EXISTS 'VASCULAR_AGE';
+ALTER TYPE "measurement_type" ADD VALUE IF NOT EXISTS 'VISCERAL_FAT';

prisma/schema.prisma

@@ -255,6 +255,14 @@ enum MeasurementType {
   WALKING_RUNNING_DISTANCE // metres — HealthKit `distanceWalkingRunning`; SI metres in DB, UI converts per locale.
   VO2_MAX // mL/(kg·min) — HealthKit `vo2Max`; one sample every few days at most.
   BODY_TEMPERATURE // celsius — HealthKit `bodyTemperature`; iOS DTO already encodes this enum value.
+  // ── v1.4.25 W5d Withings full coverage ──
+  FAT_FREE_MASS // kg — Withings meastype 5 (Body+, Body Cardio, Body Comp, Body Scan). Algorithmically = weight − fat mass.
+  FAT_MASS // kg — Withings meastype 8. Mass form of BODY_FAT (kg, not %).
+  MUSCLE_MASS // kg — Withings meastype 76. Body+ family.
+  SKIN_TEMPERATURE // celsius — Withings meastype 73 (ScanWatch dermal reading). DISTINCT from BODY_TEMPERATURE — surface temps run ~32 °C, core ~37 °C; sharing a bucket would corrupt analytics.
+  PULSE_WAVE_VELOCITY // m/s — Withings meastype 91 (Body Cardio / Body Scan). Indicator of arterial stiffness.
+  VASCULAR_AGE // years — Withings meastype 155 (Body Scan). Composite of PWV + age.
+  VISCERAL_FAT // rating — Withings meastype 170 (Body Comp / Body Scan). Withings' rating scale (1–12); not directly comparable to a percent.
 
   @@map("measurement_type")
 }