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/de.ts

@@ -1338,6 +1338,7 @@ const de: Record<string, string | { name: string; category: string }[]> = {
   'memories.immichUrl': 'Immich Server URL',
   'memories.immichApiKey': 'API-Schlüssel',
   'memories.testConnection': 'Verbindung testen',
+  'memories.testFirst': 'Verbindung zuerst testen',
   'memories.connected': 'Verbunden',
   'memories.disconnected': 'Nicht verbunden',
   'memories.connectionSuccess': 'Verbindung zu Immich hergestellt',