fix(my-space): make OrdinalLongDate timezone-stable (#3207)

Addresses revu-bot review on #3280: `date.getDate()` and
`toLocaleDateString` (no `timeZone` option) resolve in the runtime's
local timezone, so a date stored at midnight UTC rendered on a UTC−N
host could shift to the previous day — e.g. `2026-03-01T00:00:00Z`
rendered as "28ᵉ février" instead of "1ᵉʳ mars".

Switched to `getUTCDate()` + `Intl.DateTimeFormat("fr-FR", { …, timeZone: "UTC" })`
so the displayed day is always derived from the stored UTC date.

Author: Viczei

packages/app/src/modules/my-space/VerticalStepper.tsx

@@ -417,12 +417,13 @@ function DeadlineRow({ date }: { date: Date }) {
 }
 
 function OrdinalLongDate({ date }: { date: Date }) {
-	const day = date.getDate();
+	const day = date.getUTCDate();
 	const suffix = day === 1 ? "er" : "e";
-	const monthYear = date.toLocaleDateString("fr-FR", {
+	const monthYear = new Intl.DateTimeFormat("fr-FR", {
 		month: "long",
 		year: "numeric",
-	});
+		timeZone: "UTC",
+	}).format(date);
 	return (
 		<>
 			{day}