Migrate date handling from Date to Temporal API

Routine scheduling, health series, service stamps, session expiry, and
date formatting move to native Temporal (Instant / ZonedDateTime in
UTC), with ISO strings kept at DB and chart boundaries. Ambient types
in src/temporal-ambient.d.ts cover the native runtime; no polyfill.
Observable behavior and stored formats are unchanged.

1 files changed, 11 insertions, 6 deletions

diff --git a/src/lib/server/auth.ts b/src/lib/server/auth.ts
index f80eda0..3db93f0 100644
--- a/src/lib/server/auth.ts
+++ b/src/lib/server/auth.ts
@@ -30,15 +30,19 @@ export function verifyPassword(candidate: string): boolean {
 	return timingSafeEqual(actual, expected);
 }
 
-export function createSession(now = Date.now()): string {
-	const expiresAt = now + SESSION_MAX_AGE_MS;
+export function createSession(
+	now: Temporal.Instant = Temporal.Now.instant(),
+): string {
+	const expiresAt = now.add({
+		milliseconds: SESSION_MAX_AGE_MS,
+	}).epochMilliseconds;
 	const payload = String(expiresAt);
 	return `${payload}.${sign(payload)}`;
 }
 
 export function isValidSession(
 	value: string | undefined,
-	now = Date.now(),
+	now: Temporal.Instant = Temporal.Now.instant(),
 ): boolean {
 	if (!value) return false;
 
@@ -46,7 +50,8 @@ export function isValidSession(
 	if (!expiresAtText || !signature || extra) return false;
 
 	const expiresAt = Number(expiresAtText);
-	if (!Number.isSafeInteger(expiresAt) || expiresAt <= now) return false;
+	if (!Number.isSafeInteger(expiresAt) || expiresAt <= now.epochMilliseconds)
+		return false;
 
 	const expected = Buffer.from(sign(expiresAtText), 'base64url');
 	const actual = Buffer.from(signature, 'base64url');
@@ -58,7 +63,7 @@ export function isValidSession(
 export function renewSession(
 	cookies: Cookies,
 	secure: boolean,
-	now = Date.now(),
+	now: Temporal.Instant = Temporal.Now.instant(),
 ): boolean {
 	const current = cookies.get(AUTH_COOKIE_NAME);
 	if (!isValidSession(current, now)) return false;
@@ -76,7 +81,7 @@ export function renewSession(
 export function setSession(
 	cookies: Cookies,
 	secure: boolean,
-	now = Date.now(),
+	now: Temporal.Instant = Temporal.Now.instant(),
 ): void {
 	cookies.set(AUTH_COOKIE_NAME, createSession(now), {
 		path: '/',