test(e2e): target the DateField overlay and ISO mirror in the medication wizard

The course-window date field now keeps its ISO value on a hidden native
input (data-slot) and edits through a text overlay (data-testid). Fill
the overlay, then assert the committed ISO value on the hidden input.

e2e/medications-wizard-daily.spec.ts

@@ -59,6 +59,9 @@ test.describe("medication wizard — daily", () => {
 
     // Step 4 — course window (today by default).
     await expectStep(page, 4);
+    // `DateField` keeps the ISO value on a hidden native date input
+    // (data-slot), while the visible overlay paints the locale-formatted
+    // string. Assert the committed ISO value on the hidden input.
     await expect(
       page.locator('[data-slot="course-window-starts"]'),
     ).toHaveValue(/^\d{4}-\d{2}-\d{2}$/);

e2e/medications-wizard-oneshot.spec.ts

@@ -62,7 +62,15 @@ test.describe("medication wizard — one-shot", () => {
     // Step 4 — course window. Set startsOn to a deterministic date so
     // the post body assertion below is stable.
     await expectStep(page, 4);
-    await page.locator('[data-slot="course-window-starts"]').fill("2026-10-15");
+    // `DateField` rides a visible text overlay (the data-testid) that parses
+    // a typed ISO string back to the canonical value; the hidden native input
+    // (data-slot) carries the committed ISO. Type into the overlay, then blur
+    // so the parse commits.
+    await page.getByTestId("course-window-starts-field").fill("2026-10-15");
+    await page.getByTestId("course-window-starts-field").blur();
+    await expect(
+      page.locator('[data-slot="course-window-starts"]'),
+    ).toHaveValue("2026-10-15");
     await clickNext(page);
 
     // Step 5 — pick Einmalig. The path compresses to 5 steps the