feat: collapse days hides map markers, Immich test-before-save (#216)

Map markers:
- Collapsing a day in the sidebar hides its places from the map
- Places assigned to multiple days only hide when all days collapsed
- Unplanned places always stay visible

Immich settings:
- New POST /integrations/immich/test endpoint validates credentials
  without saving them
- Save button disabled until test connection passes
- Changing URL or API key resets test status
- i18n: testFirst key for all 12 languages

client/src/i18n/translations/nl.ts

@@ -1337,6 +1337,7 @@ const nl: Record<string, string> = {
   'memories.immichUrl': 'Immich Server URL',
   'memories.immichApiKey': 'API-sleutel',
   'memories.testConnection': 'Verbinding testen',
+  'memories.testFirst': 'Test eerst de verbinding',
   'memories.connected': 'Verbonden',
   'memories.disconnected': 'Niet verbonden',
   'memories.connectionSuccess': 'Verbonden met Immich',