refactor(ui): semantic status text uses material tokens instead of hardcoded colors

Finishes the feedback-conventions hygiene thread: ~30 hardcoded ImVec4 green /
red / amber literals used for success / error / warning text now use
material::Success/Error/WarningVec4(), so semantic status colors follow the
active skin and stay legible in every theme (several hardcoded greens/reds read
poorly on the light/pastel skins). Covers validate-address, transaction-details,
key-export, export-all-keys, about, the Settings confirmations/lock state, and
the encryption/decryption dialogs. Brand/logo colors and muted white/grey
(disabled) text are left as-is; dynamic-alpha animated indicators are untouched.

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

src/ui/windows/export_all_keys_dialog.cpp

@@ -117,7 +117,7 @@ void ExportAllKeysDialog::render(App* app)
         } else if (!s_status.empty()) {
             ImGui::Spacing();
             ImGui::PushTextWrapPos(0.0f);
-            ImGui::TextColored(ImVec4(0.8f, 0.3f, 0.3f, 1.0f), "%s", s_status.c_str());
+            ImGui::TextColored(material::ErrorVec4(), "%s", s_status.c_str());
             ImGui::PopTextWrapPos();
         }