feat(send): add a shared contact picker to the recipient field

Phase 0c. The Send recipient field only offered Paste and a tx-history
suggestion list — no way to pick a saved contact. Add a compact contacts
icon button next to Paste that opens a picker popup over the App-owned
address book; selecting a contact fills the recipient (re-validated next
frame).

- New header-only src/ui/windows/contact_picker.h: ContactPickerPopup(id,
  book, outBuf, outSz) — a reusable popup listing contacts ([Z]/[T] tag +
  label + short address) that copies the chosen address into the caller's
  buffer. Kept out of the material layer so the design-system headers stay
  free of data/ deps; reserved for Chat "new conversation" later.
- send_tab: shrink the recipient input to make room for the icon button
  (ICON_MD_CONTACTS), wire the popup to app->addressBook(). Coexists with the
  existing Paste + suggestion affordances.
- i18n: send_contacts_button tooltip.

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

CMakeLists.txt

@@ -595,6 +595,7 @@ set(APP_HEADERS
     src/ui/windows/qr_popup_dialog.h
     src/ui/windows/validate_address_dialog.h
     src/ui/windows/contacts_tab.h
+    src/ui/windows/contact_picker.h
     src/ui/windows/shield_dialog.h
     src/ui/windows/request_payment_dialog.h
     src/ui/windows/block_info_dialog.h

src/ui/windows/contact_picker.h

@@ -0,0 +1,65 @@
+// DragonX Wallet - ImGui Edition
+// Copyright 2024-2026 The Hush Developers
+// Released under the GPLv3
+
+#pragma once
+
+#include "imgui.h"
+#include "../../data/address_book.h"
+#include "../../util/i18n.h"
+#include "../../util/text_format.h"
+#include <cstring>
+#include <string>
+
+namespace dragonx {
+namespace ui {
+
+/**
+ * @brief Shared address-book contact picker popup.
+ *
+ * Header-only so Send (and later Chat "new conversation") can reuse it without
+ * pulling the address book into the material layer. Trigger with
+ * ImGui::OpenPopup(id) from a button, then call this every frame. On selection
+ * it copies the chosen contact's address into outBuf (NUL-terminated) and
+ * returns true.
+ *
+ * @param id      Popup id (must match the ImGui::OpenPopup(id) call).
+ * @param book    The App-owned address book (app->addressBook()).
+ * @param outBuf  Destination buffer for the chosen address.
+ * @param outSz   Size of outBuf.
+ * @return true on the frame a contact is picked.
+ */
+inline bool ContactPickerPopup(const char* id, const data::AddressBook& book,
+                               char* outBuf, size_t outSz)
+{
+    bool picked = false;
+    if (ImGui::BeginPopup(id)) {
+        if (book.empty()) {
+            ImGui::TextDisabled("%s", TR("address_book_empty"));
+        } else {
+            const auto& entries = book.entries();
+            for (size_t i = 0; i < entries.size(); ++i) {
+                const auto& e = entries[i];
+                ImGui::PushID(static_cast<int>(i));
+                // [Z]/[T] type marker (derived from the address) + label + short address.
+                const char* tag = (!e.address.empty() && e.address[0] == 'z') ? "[Z] " : "[T] ";
+                std::string shortAddr = util::truncateMiddle(e.address, 24);
+                std::string row = std::string(tag) + e.label + "  " + shortAddr;
+                if (ImGui::Selectable(row.c_str())) {
+                    if (outSz > 0) {
+                        std::strncpy(outBuf, e.address.c_str(), outSz - 1);
+                        outBuf[outSz - 1] = '\0';
+                    }
+                    picked = true;
+                    ImGui::CloseCurrentPopup();
+                }
+                ImGui::PopID();
+            }
+        }
+        ImGui::EndPopup();
+    }
+    return picked;
+}
+
+} // namespace ui
+} // namespace dragonx

src/ui/windows/send_tab.cpp

@@ -16,6 +16,7 @@
 #include "../../util/text_format.h"
 #include "../notifications.h"
 #include "../layout.h"
+#include "contact_picker.h"
 #include "../schema/ui_schema.h"
 #include "../material/type.h"
 #include "../material/draw_helpers.h"
@@ -1272,7 +1273,8 @@ void RenderSendTab(App* app)
             ImGui::Dummy(ImVec2(0, Layout::spacingSm()));
 
             float pasteW = std::max(schema::UI().drawElement("tabs.send", "paste-btn-min-width").size, colW * schema::UI().drawElement("tabs.send", "paste-btn-width-ratio").size);
-            ImGui::PushItemWidth(colW - pasteW - Layout::spacingSm());
+            float contactsW = ImGui::GetFrameHeight();  // compact square icon button for the contact picker
+            ImGui::PushItemWidth(colW - pasteW - contactsW - Layout::spacingSm() * 2.0f);
 
             // Show clipboard preview as transparent overlay when paste button is hovered
             bool paste_hovered = false;
@@ -1331,6 +1333,15 @@ void RenderSendTab(App* app)
                 }
             }
 
+            // Contact picker — pick a saved contact's address as the recipient.
+            ImGui::SameLine();
+            if (material::TactileButton(ICON_MD_CONTACTS "##pickContact", ImVec2(contactsW, 0),
+                                        material::Type().iconMed()))
+                ImGui::OpenPopup("##ContactPickerPopup");
+            if (ImGui::IsItemHovered()) material::Tooltip("%s", TR("send_contacts_button"));
+            ContactPickerPopup("##ContactPickerPopup", app->addressBook(),
+                               s_to_address, sizeof(s_to_address));
+
             // Recently sent-to suggestions
             RenderAddressSuggestions(state, colW, "##AddrSugForm");
         }

src/util/i18n.cpp

@@ -751,6 +751,7 @@ void I18n::loadBuiltinEnglish()
         // Send Tab
         strings_["pay_from"] = "Pay From";
         strings_["send_to"] = "Send To";
+        strings_["send_contacts_button"] = "Pick from contacts";
         strings_["amount"] = "Amount";
         strings_["memo"] = "Memo (optional, encrypted)";
         strings_["miner_fee"] = "Miner Fee";