feat(webmail): conversations - list, stacked reader, inline reply, settings switch

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

services/webmail/messages/en.json

@@ -548,5 +548,21 @@
     "signOutAll": "Sign out of all accounts",
     "active": "Active",
     "settings": "Account settings"
+  },
+  "conversations": {
+    "conversationView": "Group mail into conversations",
+    "conversationViewHint": "Show a message and its replies together, and whether you have answered.",
+    "messagesInConversation": "{count} messages",
+    "youReplied": "You replied",
+    "notReplied": "Not answered yet",
+    "expandAll": "Expand all",
+    "collapseOlder": "Collapse older",
+    "loadingMessage": "Loading message…",
+    "replyBelow": "Reply",
+    "conversationEmpty": "This conversation is empty.",
+    "me": "me",
+    "draftDiscarded": "Reply discarded",
+    "sentReply": "Reply sent",
+    "moreMessages": "Show {count} earlier messages"
   }
 }