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.

5 files changed, 19 insertions, 27 deletions

diff --git a/src/routes/+page.server.ts b/src/routes/+page.server.ts
index fc160df..fe9b4e3 100644
--- a/src/routes/+page.server.ts
+++ b/src/routes/+page.server.ts
@@ -5,7 +5,7 @@ import { parseFormString } from '$lib/server/services/validation';
 import type { Actions, PageServerLoad } from './$types';
 
 export const load: PageServerLoad = async () => {
-	return loadOverview(Date.now());
+	return loadOverview(Temporal.Now.instant());
 };
 
 export const actions: Actions = {
diff --git a/src/routes/projects/[id]/+page.server.ts b/src/routes/projects/[id]/+page.server.ts
index 7cb90ff..19aea9b 100644
--- a/src/routes/projects/[id]/+page.server.ts
+++ b/src/routes/projects/[id]/+page.server.ts
@@ -26,7 +26,7 @@ export const load: PageServerLoad = async ({ params }) => {
 	if (!project || project.archived) {
 		throw error(404, 'Projet introuvable');
 	}
-	const dashboard = await loadProjectDashboard(id, Date.now());
+	const dashboard = await loadProjectDashboard(id, Temporal.Now.instant());
 	const archived = await loadArchived(id);
 	return {
 		project: { id: project.id, name: project.name },
diff --git a/src/routes/projects/[id]/+page.svelte b/src/routes/projects/[id]/+page.svelte
index a58aeba..9931f40 100644
--- a/src/routes/projects/[id]/+page.svelte
+++ b/src/routes/projects/[id]/+page.svelte
@@ -9,6 +9,7 @@
 		parseIntervalToDays,
 		type RoutineState,
 	} from '$lib/shared/routine-metrics';
+	import { formatDayMonth } from '$lib/shared/temporal';
 
 	let { data, form } = $props();
 
@@ -30,11 +31,6 @@
 			: matchItems(data.archived, archiveFilter).map((m) => m.obj),
 	);
 
-	const dateFormatter = new Intl.DateTimeFormat('fr-FR', {
-		day: 'numeric',
-		month: 'short',
-	});
-
 	function sorted(routines: RoutineState[]): RoutineState[] {
 		return [...routines].sort(
 			(a, b) => b.overdueRatio - a.overdueRatio || a.name.localeCompare(b.name),
@@ -182,7 +178,7 @@
 						<span class="routine-meta">
 							{formatFrequency(routine.frequencyDays)}
 							{#if routine.lastDoneAt}
-								· fait le {dateFormatter.format(new Date(routine.lastDoneAt))}
+								· fait le {formatDayMonth(routine.lastDoneAt)}
 							{:else}
 								· jamais fait
 							{/if}
@@ -244,7 +240,7 @@
 							>
 							<span class="archived-date">
 								{formatFrequency(routine.frequencyDays)} · archivée le
-								{dateFormatter.format(new Date(routine.archivedAt))}
+								{formatDayMonth(routine.archivedAt)}
 							</span>
 						</li>
 					{/each}
diff --git a/src/routes/projects/[projectId]/routine/[routineId]/+page.server.ts b/src/routes/projects/[projectId]/routine/[routineId]/+page.server.ts
index df4c2cc..bdfa452 100644
--- a/src/routes/projects/[projectId]/routine/[routineId]/+page.server.ts
+++ b/src/routes/projects/[projectId]/routine/[routineId]/+page.server.ts
@@ -26,7 +26,9 @@ export const load: PageServerLoad = async ({ params }) => {
 	const completions = await loadCompletions(routineId);
 	// An archived routine is frozen at its archive instant: state and chart
 	// stop there instead of now.
-	const at = routine.archivedAt ? Date.parse(routine.archivedAt) : Date.now();
+	const at = routine.archivedAt
+		? Temporal.Instant.from(routine.archivedAt)
+		: Temporal.Now.instant();
 	return {
 		project: { id: project.id, name: project.name },
 		routine,
diff --git a/src/routes/projects/[projectId]/routine/[routineId]/+page.svelte b/src/routes/projects/[projectId]/routine/[routineId]/+page.svelte
index ab2644d..e593ad1 100644
--- a/src/routes/projects/[projectId]/routine/[routineId]/+page.svelte
+++ b/src/routes/projects/[projectId]/routine/[routineId]/+page.svelte
@@ -8,6 +8,7 @@
 		parseIntervalToDays,
 		computeHealthSeries,
 	} from '$lib/shared/routine-metrics';
+	import { formatDayMonth, formatDayMonthYear } from '$lib/shared/temporal';
 	let { data, form } = $props();
 	let name = $state('');
 	let frequency = $state('');
@@ -27,24 +28,19 @@
 		}
 	});
 	const frequencyDays = $derived(parseIntervalToDays(frequency));
-	const dateFormatter = new Intl.DateTimeFormat('fr-FR', {
-		day: 'numeric',
-		month: 'short',
-	});
-	const dateTimeFormatter = new Intl.DateTimeFormat('fr-FR', {
-		day: 'numeric',
-		month: 'short',
-		year: 'numeric',
-	});
 	const frozenAt = $derived(
 		data.routine.archived
-			? Date.parse(data.routine.archivedAt ?? data.routine.createdAt)
-			: Date.now(),
+			? Temporal.Instant.from(data.routine.archivedAt ?? data.routine.createdAt)
+			: Temporal.Now.instant(),
 	);
 	const series = $derived(
 		computeHealthSeries(data.routine, data.completions, frozenAt),
 	);
-	const markers = $derived(data.completions.map((c) => Date.parse(c.doneAt)));
+	const markers = $derived(
+		data.completions.map(
+			(c) => Temporal.Instant.from(c.doneAt).epochMilliseconds,
+		),
+	);
 </script>
 
 <main>
@@ -60,9 +56,7 @@
 	{#if data.routine.archived}
 		<p class="archived-badge">
 			Archivée le
-			{dateTimeFormatter.format(
-				new Date(data.routine.archivedAt ?? data.routine.createdAt),
-			)}
+			{formatDayMonthYear(data.routine.archivedAt ?? data.routine.createdAt)}
 		</p>
 	{/if}
 
@@ -144,7 +138,7 @@
 				<span class="chart-meta">
 					{formatFrequency(data.routine.frequencyDays)}
 					{#if data.state.lastDoneAt}
-						· fait le {dateFormatter.format(new Date(data.state.lastDoneAt))}
+						· fait le {formatDayMonth(data.state.lastDoneAt)}
 					{:else}
 						· jamais fait
 					{/if}
@@ -182,7 +176,7 @@
 		{#each data.completions as c (c.id)}
 			<li class="item-row item-row--card completion-row">
 				<span class="completion-date">
-					{dateTimeFormatter.format(new Date(c.doneAt))}
+					{formatDayMonthYear(c.doneAt)}
 				</span>
 				{#if c.note}
 					<span class="completion-note">{c.note}</span>