Fix double delete confirm, inline place name editing, preserve assignments on trip extend

- Replace double browser confirm() with single custom ConfirmDialog for place deletion
- Add inline name editing via double-click in PlaceInspector
- Rewrite generateDays() to preserve existing days/assignments when extending trips
- Use UTC date math to avoid timezone-related day count errors
- Add missing collab.chat.emptyDesc translation (en/de)

client/src/i18n/translations/de.js

@@ -956,6 +956,7 @@ const de = {
   'collab.chat.placeholder': 'Nachricht eingeben...',
   'collab.chat.empty': 'Starte die Unterhaltung',
   'collab.chat.emptyHint': 'Nachrichten werden mit allen Reiseteilnehmern geteilt',
+  'collab.chat.emptyDesc': 'Teile Ideen, Pläne und Updates mit deiner Reisegruppe',
   'collab.chat.today': 'Heute',
   'collab.chat.yesterday': 'Gestern',
   'collab.chat.deletedMessage': 'hat eine Nachricht gelöscht',

client/src/i18n/translations/en.js

@@ -956,6 +956,7 @@ const en = {
   'collab.chat.placeholder': 'Type a message...',
   'collab.chat.empty': 'Start the conversation',
   'collab.chat.emptyHint': 'Messages are shared with all trip members',
+  'collab.chat.emptyDesc': 'Share ideas, plans, and updates with your travel group',
   'collab.chat.today': 'Today',
   'collab.chat.yesterday': 'Yesterday',
   'collab.chat.deletedMessage': 'deleted a message',