feat(chat): copy, add-to-contacts, and new-message toast (Q2/Q3/Q4)

- Q3: copy the peer z-address from the thread header (SmallButton), and right-click
  any message to copy its body.
- Q2: an "Add contact" action in the header when the peer isn't already known —
  one click saves them to the address book (rename later in Contacts).
- Q4: capture ChatService::ingest's new-message count (previously discarded) and
  fire an in-app toast when new encrypted chat arrives while the user isn't on the
  Chat tab (main-thread MainCb sites only).

i18n (EN + 8 languages, additive; no new CJK glyphs).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ui/windows/chat_tab.cpp

@@ -16,6 +16,7 @@
 #include "../material/draw_helpers.h"  // TactileButton / LabeledInput / BeginOverlayDialog
 #include "../material/project_icons.h" // ICON_MD_*
 #include "../layout.h"   // Layout::dpiScale()
+#include "../notifications.h"          // Notifications — add-to-contacts confirmation
 #include "imgui.h"
 
 #include <sodium.h>      // sodium_memzero — wipe typed plaintext on a wallet switch
@@ -284,6 +285,16 @@ void RenderChatTab(App* app)
                 ImGui::TextUnformatted(shorten(sel->peerZaddr, 20, 12).c_str());
                 ImGui::PopStyleColor();
                 ImGui::PopFont();
+                // Header actions: copy the peer z-address (Q3), and add them to contacts when unknown (Q2).
+                if (ImGui::SmallButton(TR("copy_address"))) ImGui::SetClipboardText(sel->peerZaddr.c_str());
+                if (book.findByAddress(sel->peerZaddr) < 0) {
+                    ImGui::SameLine();
+                    if (ImGui::SmallButton(TR("chat_add_contact"))) {
+                        data::AddressBookEntry e(sel->peerName, sel->peerZaddr);  // label = shortened addr; rename in Contacts
+                        if (book.addEntry(e)) Notifications::instance().success(TR("chat_contact_added"));
+                        else                  Notifications::instance().error(TR("address_book_exists"));
+                    }
+                }
             }
             ImGui::Separator();
 
@@ -291,7 +302,9 @@ void RenderChatTab(App* app)
             ImGui::BeginChild("##ChatMessages", ImVec2(0, ImGui::GetContentRegionAvail().y - footerH), false);
             {
                 const auto messages = store.conversation(s_selected_cid);
-                for (const auto& m : messages) {
+                for (std::size_t mi = 0; mi < messages.size(); ++mi) {
+                    const auto& m = messages[mi];
+                    ImGui::PushID(static_cast<int>(mi));
                     const bool outgoing = (m.direction == chat::ChatDirection::Outgoing);
                     const bool request = (m.kind == chat::ChatMessageKind::ContactRequest);
                     const bool failed = outgoing && m.delivery == chat::ChatDelivery::Failed;
@@ -307,13 +320,20 @@ void RenderChatTab(App* app)
                     ImGui::TextUnformatted(who.c_str());
                     ImGui::PopStyleColor();
                     ImGui::PopFont();
-                    // Body (wrapped).
+                    // Body (wrapped). Right-click to copy (Q3).
                     ImGui::PushFont(nameFont);
                     ImGui::PushTextWrapPos(0.0f);
                     ImGui::TextWrapped("%s", m.body.c_str());
                     ImGui::PopTextWrapPos();
                     ImGui::PopFont();
+                    if (ImGui::IsItemHovered() && ImGui::IsMouseClicked(ImGuiMouseButton_Right))
+                        ImGui::OpenPopup("##msgmenu");
+                    if (ImGui::BeginPopup("##msgmenu")) {
+                        if (ImGui::MenuItem(TR("copy"))) ImGui::SetClipboardText(m.body.c_str());
+                        ImGui::EndPopup();
+                    }
                     ImGui::Dummy(ImVec2(0.0f, 6.0f));
+                    ImGui::PopID();
                 }
                 if (s_scroll_to_cid == s_selected_cid) {
                     ImGui::SetScrollHereY(1.0f);