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, 54 insertions, 0 deletions

diff --git a/src/temporal-ambient.d.ts b/src/temporal-ambient.d.ts
new file mode 100644
index 0000000..f6080b0
--- /dev/null
+++ b/src/temporal-ambient.d.ts
@@ -0,0 +1,54 @@
+// Minimal ambient Temporal declarations (native runtime, no polyfill).
+// Covers only what this app uses; extend as needed. If a future TS lib
+// ships Temporal types, these merge with them.
+
+declare global {
+	namespace Temporal {
+		type TimeZoneId = string;
+		type DurationLike = {
+			days?: number;
+			hours?: number;
+			milliseconds?: number;
+		};
+
+		interface Duration {
+			total(options: { unit: 'millisecond' | 'day' }): number;
+		}
+		namespace Duration {
+			function from(durationLike: DurationLike): Duration;
+		}
+
+		interface Instant {
+			readonly epochMilliseconds: number;
+			add(durationLike: { hours?: number; milliseconds?: number }): Instant;
+			toString(options?: { smallestUnit?: 'millisecond' }): string;
+			toZonedDateTimeISO(timeZone: TimeZoneId): ZonedDateTime;
+			toLocaleString(
+				locales?: string | string[],
+				options?: Intl.DateTimeFormatOptions,
+			): string;
+		}
+		namespace Instant {
+			function compare(a: string | Instant, b: string | Instant): number;
+			function from(iso: string): Instant;
+			function fromEpochMilliseconds(ms: number): Instant;
+		}
+
+		interface ZonedDateTime {
+			add(durationLike: DurationLike): ZonedDateTime;
+			startOfDay(): ZonedDateTime;
+			toInstant(): Instant;
+			toLocaleString(
+				locales?: string | string[],
+				options?: Intl.DateTimeFormatOptions,
+			): string;
+		}
+
+		namespace Now {
+			function instant(): Instant;
+			function timeZoneId(): TimeZoneId;
+		}
+	}
+}
+
+export {};