feat: add What's new feature

Dashboard dialog shows unseen news entries. Users mark them seen with "Got it"
or revisit via the /whats-new page. Admins publish, edit, and delete entries
on /admin/news. Full i18n support and test coverage included.

public/i18n/en.json

@@ -297,6 +297,8 @@
       "ERROR": "The role could not be switched."
     },
     "ADMIN_HINTS": "Hints",
+    "WHATS_NEW": "What's new",
+    "ADMIN_NEWS": "News",
     "PENDING_REQUESTS_one": "{{count}} registration waits",
     "PENDING_REQUESTS_other": "{{count}} registrations wait"
   },
@@ -626,6 +628,37 @@
     "DONE_COUNT_one": "Closed for good by {{count}} user",
     "DONE_COUNT_other": "Closed for good by {{count}} users"
   },
+  "NEWS": {
+    "TITLE": "What's new",
+    "GOT_IT": "Got it",
+    "SAVE_FAILED": "Could not save that you read the news.",
+    "LOAD_ERROR": "The news could not be loaded.",
+    "EMPTY": "Nothing new yet."
+  },
+  "ADMIN_NEWS": {
+    "NEW": "New entry",
+    "EDIT": "Edit entry",
+    "TITLE_EN": "Title (English)",
+    "TITLE_DE": "Title (German, optional)",
+    "TEXT_EN": "Text (English)",
+    "TEXT_DE": "Text (German, optional)",
+    "TEXT_HELP": "Plain text. Title max 100, text max 2000 characters. Without a German text, German users see the English one.",
+    "PREVIEW": "Preview",
+    "CREATE": "Publish",
+    "SAVE": "Save",
+    "CANCEL": "Cancel",
+    "CREATED": "Entry published.",
+    "UPDATED": "Entry saved.",
+    "DELETED": "Entry deleted.",
+    "EDIT_ACTION": "Edit",
+    "DELETE": "Delete",
+    "CONFIRM_DELETE": "Delete this entry for everyone?",
+    "ERROR": "The action failed.",
+    "LIST": "All entries",
+    "EMPTY": "No entries yet.",
+    "LOAD_ERROR": "The entries could not be loaded.",
+    "NO_ACCESS": "Only admins can open this page."
+  },
   "TILES": {
     "CUSTOMIZE": "Customize",
     "EDIT_HINT": "Move, resize or hide the tiles. Nothing is saved before \"Done\".",