feat(backup): carry per-schedule units-per-dose through backup and restore

The schedule exporter enumerates columns, so the new per-schedule
units-per-dose needs adding by hand: export it as a Decimal string in
the disaster-recovery payload, accept it in the wire schema, and write
it back on restore (NULL stays NULL to inherit). Extend the round-trip
test to prove a half-tablet slot survives export and re-import.

src/lib/export/__tests__/full-backup-payload.test.ts

@@ -131,6 +131,8 @@ function makePrisma() {
               scheduleType: "CYCLIC",
               cyclicOnWeeks: 3,
               cyclicOffWeeks: 1,
+              // #219 — per-schedule units per dose (a half tablet at this slot).
+              unitsPerDose: { toString: () => "0.5000" },
               doseWindows: [
                 { timeOfDay: "08:00", start: "07:30", end: "09:00" },
               ],
@@ -502,6 +504,8 @@ describe("buildFullBackupPayload disaster-recovery mode", () => {
               scheduleType: "CYCLIC",
               cyclicOnWeeks: 3,
               cyclicOffWeeks: 1,
+              // #219 — Decimal → string, round-tripped through the DR payload.
+              unitsPerDose: "0.5000",
             }),
           ],
         }),

src/lib/export/full-backup-payload.ts

@@ -507,6 +507,10 @@ export async function buildFullBackupPayload(
               cyclicOnWeeks: s.cyclicOnWeeks,
               cyclicOffWeeks: s.cyclicOffWeeks,
               doseWindows: s.doseWindows,
+              // #219 — per-schedule units per dose. Decimal → string like the
+              // medication-level column; NULL (inherit) stays NULL.
+              unitsPerDose:
+                s.unitsPerDose == null ? null : s.unitsPerDose.toString(),
             }
           : {}),
         windowStart: s.windowStart,