Anchor the sync fixtures on a relative clock

The sync-changes fixtures seeded rows at a literal calendar date. The route
serves only what sits inside the tombstone retention horizon, which is sixty
days plus a fifteen-day margin, so the fixture was inside the window when it
was written and fell out of it exactly seventy-five days later. Three cursor
round-trips started failing at midnight with no commit behind them, and would
have failed on every run from then on.

The rows now anchor five days before the current time, so they cannot age out
of the window they are meant to be inside. The mood entry's own date string is
derived from the same anchor rather than written out, because the two drifting
apart is the same defect one level down.

tests/integration/sync-changes.test.ts

@@ -115,10 +115,29 @@ interface ChangesData {
   };
 }
 
+/**
+ * The fixture clock: a few days ago, never a fixed calendar date.
+ *
+ * These rows have to sit INSIDE the sync retention horizon
+ * (`TOMBSTONE_RETENTION_DAYS`, 60 + 15 = 75 days) or the route correctly
+ * refuses to serve them and the first page comes back empty. The literal date
+ * this file used to carry satisfied that when it was written and stopped
+ * satisfying it exactly 75 days later: the suite went red at midnight with no
+ * commit behind it, and would have stayed red for good. Anchoring on
+ * `Date.now()` is what stops a fixture ageing out of the window it is meant to
+ * be inside.
+ */
+const FIXTURE_BASE_MS = Date.now() - 5 * 86_400_000;
+
+/** The fixture day for row `i`, as the `YYYY-MM-DD` a mood entry stores. */
+function fixtureDay(i: number): string {
+  return new Date(FIXTURE_BASE_MS + i * 86_400_000).toISOString().slice(0, 10);
+}
+
 /** Seed n live measurements with strictly increasing updatedAt. */
 async function seedLive(n: number): Promise<void> {
   const prisma = getPrismaClient();
-  const base = new Date("2026-05-20T00:00:00.000Z").getTime();
+  const base = FIXTURE_BASE_MS;
   for (let i = 0; i < n; i++) {
     await prisma.measurement.create({
       data: {
@@ -138,13 +157,13 @@ async function seedLive(n: number): Promise<void> {
 /** Seed n live mood entries with strictly increasing updatedAt. */
 async function seedMood(n: number): Promise<string[]> {
   const prisma = getPrismaClient();
-  const base = new Date("2026-05-20T00:00:00.000Z").getTime();
+  const base = FIXTURE_BASE_MS;
   const ids: string[] = [];
   for (let i = 0; i < n; i++) {
     const row = await prisma.moodEntry.create({
       data: {
         userId: TEST_USER_ID,
-        date: `2026-05-${20 + i}`,
+        date: fixtureDay(i),
         mood: "GUT",
         score: 4,
         moodLoggedAt: new Date(base + i * 60_000),
@@ -161,7 +180,7 @@ async function seedIntakes(
   n: number,
 ): Promise<{ medId: string; ids: string[] }> {
   const prisma = getPrismaClient();
-  const base = new Date("2026-05-20T00:00:00.000Z").getTime();
+  const base = FIXTURE_BASE_MS;
   const med = await prisma.medication.create({
     data: {
       userId: TEST_USER_ID,
@@ -233,7 +252,7 @@ describe("GET /api/sync/changes (real Postgres)", () => {
 
   it("surfaces a soft-deleted measurement as a tombstone, never as an upsert", async () => {
     const prisma = getPrismaClient();
-    const base = new Date("2026-05-20T00:00:00.000Z").getTime();
+    const base = FIXTURE_BASE_MS;
     await prisma.measurement.create({
       data: {
         userId: TEST_USER_ID,