refactor(settings): drop the redundant "Key" label above the import field

The "Import Private Key" / "Import Viewing Key" dialog heading already gives the
context, so the "Key" / "Viewing key" label above the input was redundant. Remove
it; the field is the dialog's primary input and reads fine without it.

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

src/app.cpp

@@ -2896,10 +2896,10 @@ void App::renderImportKeyDialog()
         ImGui::Spacing();
     }
 
-    // Masked key field; the reveal (eye) toggle sits frameless flush at its right edge, with labelled
-    // Paste / Clear buttons beneath. Hovering Paste previews the clipboard INSIDE the field (masked
-    // with '*' unless the key is revealed) — like the send tab — so the user can verify before pasting.
-    ImGui::TextUnformatted(viewMode ? TR("import_viewkey_field") : TR("import_key_field"));
+    // Masked key field (no "Key" label — the dialog heading already gives the context); the reveal
+    // (eye) toggle sits frameless flush at its right edge, with labelled Paste / Clear buttons beneath.
+    // Hovering Paste previews the clipboard INSIDE the field (masked with '*' unless the key is
+    // revealed) — like the send tab — so the user can verify before pasting.
     const float fieldH = ImGui::GetFrameHeight();
     const ImVec2 iconSz(fieldH, fieldH);
     ImGui::SetNextItemWidth(ImGui::GetContentRegionAvail().x - fieldH);