feat(chat): "Request" pill on unsolicited conversations in the list

The conversation list now marks a pending stranger request with a small
"Request" pill (bottom-right of the row), so it's distinguishable before you
open it; the preview text is clipped to the pill's left so they don't overlap.
Completes the request-affordance pair with the in-thread Accept/Block card.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/util/i18n.cpp

@@ -232,6 +232,7 @@ void I18n::loadBuiltinEnglish()
         strings_["chat_empty_hint"] = "No conversations yet. Messages you receive will appear here.";
         strings_["chat_you"] = "You";
         strings_["chat_contact_request"] = "contact request";
+        strings_["chat_request_pill"] = "Request";
         strings_["chat_request_title"] = "New contact request";
         strings_["chat_request_body"] = "This person isn't in your contacts. Accept to add them, or block to delete this conversation and ignore them.";
         strings_["chat_request_accept"] = "Accept";