notifications: timezone fix + configurable site timezone

shopdb/core/api/settings.py

@@ -56,6 +56,7 @@ PUBLIC_SETTING_CATEGORIES = {'branding', 'map'}
 PUBLIC_SETTING_KEYS = {
     'site_base_url', 'facility_name', 'printer_hostname_template',
     'contact_email_domain', 'servicenow_enabled', 'setup_complete',
+    'site_timezone',
 }
 
 
@@ -443,6 +444,13 @@ def build_default_settings():
             'category': 'site',
             'description': 'Set true once the first-run setup wizard has been finished'
         },
+        {
+            'key': 'site_timezone',
+            'value': 'America/New_York',
+            'valuetype': 'string',
+            'category': 'site',
+            'description': "IANA timezone for this site (e.g. America/New_York, America/Chicago). Notification start/end times and daily-reset expiry are computed in this zone."
+        },
         {
             'key': 'employee_directory_mode',
             'value': 'selfhosted',