test: name the shared glucose factor where the CSV import pinned the old one

Three assertions repeated 18.016 and the product it gave. They were the
reason the two factors could sit in the tree at once looking correct. They
take the exported constant now, and the parser test asserts the round trip
a reader on mmol/L experiences rather than a magic product.

src/app/api/import/csv/__tests__/route.test.ts

@@ -59,6 +59,7 @@ vi.mock("@/lib/rollups/measurement-rollups", async () => {
 
 import { NextRequest } from "next/server";
 import { POST } from "../route";
+import { MGDL_PER_MMOL } from "@/lib/glucose";
 import { checkRateLimit } from "@/lib/rate-limit";
 import { prisma } from "@/lib/db";
 import { recomputeBucketsForMeasurement } from "@/lib/rollups/measurement-rollups";
@@ -369,7 +370,7 @@ describe("POST /api/import/csv — contextless blood glucose", () => {
       externalId: "sensor-1",
       glucoseContext: null,
     });
-    expect(row.value).toBeCloseTo(95.4848, 3);
+    expect(row.value).toBeCloseTo(5.3 * MGDL_PER_MMOL, 3);
     expect((row.measuredAt as Date).toISOString()).toBe(
       "2024-04-03T02:15:00.000Z",
     );

src/lib/import/__tests__/csv-measurements.test.ts

@@ -1,4 +1,5 @@
 import { describe, it, expect } from "vitest";
+import { MGDL_PER_MMOL, mgdlToMmol } from "@/lib/glucose";
 
 import {
   parseCsvMeasurements,
@@ -98,7 +99,12 @@ describe("parseCsvMeasurements — unit conversion", () => {
     ]);
     expect(out.rows[0].status).toBe("ok");
     expect(out.rows[0].row?.unit).toBe("mg/dL");
-    expect(out.rows[0].row?.value).toBeCloseTo(5.3 * 18.016, 3);
+    // The one factor the app converts glucose by, both directions. The
+    // literal that used to sit here was 18.016 while every display path
+    // divided by 18.0182, so a reading imported in mmol/L did not read back
+    // as the number it went in as.
+    expect(out.rows[0].row?.value).toBeCloseTo(5.3 * MGDL_PER_MMOL, 3);
+    expect(mgdlToMmol(out.rows[0].row?.value ?? 0)).toBe(5.3);
   });
 
   it("converts weight lb to canonical kg", () => {
@@ -176,7 +182,7 @@ describe("parseCsvMeasurements — glucose context", () => {
     for (const result of out.rows) {
       expect(result.row).not.toHaveProperty("glucoseContext");
       expect(result.row?.unit).toBe("mg/dL");
-      expect(result.row?.value).toBeCloseTo(95.4848, 3);
+      expect(result.row?.value).toBeCloseTo(5.3 * MGDL_PER_MMOL, 3);
     }
     expect(out.rows[0].row?.measuredAt.toISOString()).toBe(
       "2024-04-03T02:15:00.000Z",