immich-frame: set photo date format to dd/MM/yyyy

The photo date overlay was showing US-style MM/dd/yyyy — ImmichFrame's built-in default when PhotoDateFormat is unset. Viktor wants UK day/month/year ordering instead. Pin PhotoDateFormat to the date-fns pattern "dd/MM/yyyy" (uppercase MM = month; lowercase mm would render minutes). The config map carries reloader.stakater.com/match, so Reloader restarts the immich-frame pod automatically on apply.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

stacks/immich/frame.tf

@@ -22,6 +22,7 @@ resource "kubernetes_config_map" "mailserver_config" {
         ShowAlbumName: false
         ShowProgressBar: false
         ClockFormat: "HH:mm"
+        PhotoDateFormat: "dd/MM/yyyy"
         WeatherApiKey: ${data.vault_kv_secret_v2.secrets.data["frame_weather_api_key"]}
         UnitSystem: metric
         WeatherLatLong: "51.5074,-0.1278"