test(plant-hours): cover unknown-QR deviation + value rounding

Adds two tests that lock in behaviour the previous test file relied on
implicitly:
- validatePlantHoursRow rejects when the supplied vehicle's qr_code_id
  doesn't match row.vehicle_qr (the guard the schema extends beyond
  the original spec)
- computePlantHoursFields rounds value to 2 decimal places (a
  fractional-input case the integer-only assertion didn't exercise)

src/lib/plant-hours-schema.test.ts

@@ -41,6 +41,17 @@ describe("computePlantHoursFields", () => {
     expect(computePlantHoursFields(validRow).value).toBe(5735);
     // 31 * 185 = 5735 exactly
   });
+  it("rounds value to 2 decimal places", () => {
+    // 31.5 * 185.25 = 5835.375, rounds to 5835.38
+    const r = computePlantHoursFields({
+      ...validRow,
+      start_hours: 1200,
+      end_hours: 1231.5,
+      hours: 31.5,
+      cost_per_hour: 185.25,
+    });
+    expect(r.value).toBe(5835.38);
+  });
   it("flags over_budget when hours > hour_meter_budget", () => {
     expect(computePlantHoursFields(validRow).over_budget).toBe(false);
     expect(
@@ -72,6 +83,15 @@ describe("validatePlantHoursRow", () => {
     expect(r.errors[0]).toMatch(/unknown_vehicle_qr/);
   });
 
+  it("rejects when supplied vehicle's QR doesn't match row QR", () => {
+    const r = validatePlantHoursRow(
+      validRow,  // vehicle_qr is "QR-A"
+      { ...baseVehicle, qr_code_id: "QR-Z" },  // vehicle is defined but QR doesn't match
+      new Set(),
+    );
+    expect(r.errors[0]).toMatch(/unknown_vehicle_qr/);
+  });
+
   it("rejects end_date < start_date", () => {
     const r = validatePlantHoursRow(
       { ...validRow, end_date: "2026-08-23" },