refactor: update sleep session logic, models, and agent protocols

frontend/src/components/stats/SessionList.tsx

@@ -4,7 +4,7 @@ import { useSettings } from '../../hooks/useSettings';
 import { Pagination } from './Pagination';
 import { Edit2, Check, X, Trash2 } from 'lucide-react';
 import type { SleepSessionRead } from '../../types';
-import { formatDateTime, toLocalDatetimeInputValue, getDurationMinutes, formatMinutes } from '../../utils/time';
+import { formatDateTime, toLocalDatetimeInputValue, getDurationMinutes, formatMinutes, toUTCFromLocalInput } from '../../utils/time';
 
 export function SessionList() {
   const { sessions, isLoading, updateSession, deleteSession, isDeleting } = useSessions();
@@ -29,13 +29,13 @@ export function SessionList() {
 
   const handleSave = async (id: number) => {
     try {
-       await updateSession({
-         sessionId: id,
-         payload: {
-           start_time: new Date(editStart).toISOString(),
-           end_time: editEnd ? new Date(editEnd).toISOString() : undefined,
-         }
-       });
+      await updateSession({
+        sessionId: id,
+        payload: {
+          start_time: toUTCFromLocalInput(editStart),
+          end_time: editEnd ? toUTCFromLocalInput(editEnd) : undefined,
+        },
+      });
       setEditingId(null);
     } catch (err) {
       console.error(err);

frontend/src/utils/time.ts

@@ -38,9 +38,15 @@ export function adjustForTimezone(utcMinutes: number): number {
  * @returns string in "YYYY-MM-DDTHH:MM" format
  */
 export function toLocalDatetimeInputValue(date: Date): string {
-  const offset = date.getTimezoneOffset() * 60 * 1000;
-  const localDate = new Date(date.getTime() - offset);
-  return localDate.toISOString().slice(0, 16);
+  const formatter = new Intl.DateTimeFormat('sv-SE', {
+    year: 'numeric',
+    month: '2-digit',
+    day: '2-digit',
+    hour: '2-digit',
+    minute: '2-digit',
+    hour12: false,
+  });
+  return formatter.format(date).replace(' ', 'T');
 }
 
 export function formatElapsedTime(utcTimestamp: string): string {