fix(security): color seed-save by outcome; explain the Encrypt button; friendly key-export errors

- Seed-backup dialog: a failed "Save to file" was drawn in the success (green)
  colour; it's now red on failure, green on success (flag reset on close).
- Encrypt-wallet dialog: the disabled Encrypt button now says why once the user
  starts typing ("Use at least 8 characters." / "The passphrases don't match."),
  and a "Show passphrase" checkbox reveals both fields.
- Key-export dialog: the raw RPC exception (e.g. "...walletpassphrase first")
  is routed through util::friendlyRpcError(), so a locked wallet reads
  "Unlock your wallet first, then try again." instead of daemon jargon.

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

src/app.cpp

@@ -4635,6 +4635,7 @@ void App::renderSeedBackupDialog()
             sodium_memzero(&seed_backup_phrase_[0], seed_backup_phrase_.size());
         seed_backup_phrase_.clear();
         seed_backup_status_.clear();
+        seed_backup_status_ok_ = true;
         seed_backup_fetch_started_ = false;
         seed_backup_loading_ = false;
         seed_backup_no_mnemonic_ = false;
@@ -4707,7 +4708,9 @@ void App::renderSeedBackupDialog()
         ImGui::Spacing();
         if (!seed_backup_status_.empty()) {
             ImGui::PushTextWrapPos(0.0f);
-            ImGui::TextColored(ui::material::SuccessVec4(), "%s", seed_backup_status_.c_str());
+            ImGui::TextColored(seed_backup_status_ok_ ? ui::material::SuccessVec4()
+                                                      : ImVec4(0.85f, 0.33f, 0.33f, 1.0f),
+                               "%s", seed_backup_status_.c_str());
             ImGui::PopTextWrapPos();
             ImGui::Spacing();
         }
@@ -4724,6 +4727,7 @@ void App::renderSeedBackupDialog()
             const bool ok = util::Platform::writeFileAtomically(path, content,
                                                                /*restrictPermissions=*/true);
             sodium_memzero(&content[0], content.size());
+            seed_backup_status_ok_ = ok;   // red when the write failed (was always green before)
             seed_backup_status_ = (ok ? std::string(TR("seed_backup_saved"))
                                       : std::string(TR("seed_backup_save_failed"))) + path;
         }

src/app.h

@@ -1402,6 +1402,7 @@ private:
     // mnemonic) and is wiped with sodium_memzero when the dialog closes.
     std::string seed_backup_phrase_;
     std::string seed_backup_status_;
+    bool        seed_backup_status_ok_ = true;   // colour the status line by outcome (green save vs red fail)
     bool seed_backup_fetch_started_ = false;
     bool seed_backup_loading_ = false;
     bool seed_backup_no_mnemonic_ = false;

src/app_security.cpp

@@ -1452,15 +1452,16 @@ void App::renderEncryptWalletDialog() {
 
                 ImGui::TextUnformatted(TR("wiz_passphrase"));
                 ImGui::PushItemWidth(-1);
-                ImGui::InputText("##enc_pass", encrypt_pass_buf_, sizeof(encrypt_pass_buf_),
-                                 ImGuiInputTextFlags_Password);
+                static bool s_showEncPass = false;
+                const ImGuiInputTextFlags encPwFlags = s_showEncPass ? 0 : ImGuiInputTextFlags_Password;
+                ImGui::InputText("##enc_pass", encrypt_pass_buf_, sizeof(encrypt_pass_buf_), encPwFlags);
                 ImGui::PopItemWidth();
 
                 ImGui::TextUnformatted(TR("enc_confirm"));
                 ImGui::PushItemWidth(-1);
-                ImGui::InputText("##enc_confirm", encrypt_confirm_buf_, sizeof(encrypt_confirm_buf_),
-                                 ImGuiInputTextFlags_Password);
+                ImGui::InputText("##enc_confirm", encrypt_confirm_buf_, sizeof(encrypt_confirm_buf_), encPwFlags);
                 ImGui::PopItemWidth();
+                ImGui::Checkbox(TR("enc_show_pass"), &s_showEncPass);
 
                 // Strength meter bar
                 {
@@ -1508,8 +1509,15 @@ void App::renderEncryptWalletDialog() {
                 }
 
                 ImGui::Spacing();
-                bool valid = strlen(encrypt_pass_buf_) >= 8 &&
-                             strcmp(encrypt_pass_buf_, encrypt_confirm_buf_) == 0;
+                const size_t encPassLen = strlen(encrypt_pass_buf_);
+                const bool encMatch = strcmp(encrypt_pass_buf_, encrypt_confirm_buf_) == 0;
+                bool valid = encPassLen >= 8 && encMatch;
+                // Say WHY the button is disabled, once the user has started typing (was silent before).
+                if (!valid && (encPassLen > 0 || strlen(encrypt_confirm_buf_) > 0)) {
+                    const char* why = (encPassLen < 8) ? TR("enc_min_len")
+                                    : (!encMatch ? TR("enc_mismatch") : "");
+                    if (*why) ImGui::TextColored(ImVec4(1.0f, 0.7f, 0.3f, 1.0f), "%s", why);
+                }
 
                 float btnW = (ImGui::GetContentRegionAvail().x - ImGui::GetStyle().ItemSpacing.x) * 0.5f;
                 ImGui::BeginDisabled(!valid || encrypt_in_progress_);

src/ui/windows/key_export_dialog.cpp

@@ -197,7 +197,7 @@ void KeyExportDialog::render(App* app)
                                     s_key = key;
                                     s_show_key = false;  // Don't show by default
                                 } else {
-                                    s_error = error;
+                                    s_error = util::friendlyRpcError(error);
                                 }
                                 if (!key.empty()) sodium_memzero(&key[0], key.size());  // wipe the last transient copy
                                 s_fetching = false;
@@ -223,7 +223,7 @@ void KeyExportDialog::render(App* app)
                                         s_key = key;
                                         s_show_key = true;  // Viewing keys are less sensitive
                                     } else {
-                                        s_error = error;
+                                        s_error = util::friendlyRpcError(error);
                                     }
                                     if (!key.empty()) sodium_memzero(&key[0], key.size());  // wipe the last transient copy
                                     s_fetching = false;

src/util/i18n.cpp

@@ -697,6 +697,9 @@ void I18n::loadBuiltinEnglish()
         // --- Encrypt / change-passphrase dialogs (settings) ---
         strings_["enc_desc"] = "Encrypting your wallet protects your private keys with a passphrase. After encryption, the daemon will restart.";
         strings_["enc_confirm"] = "Confirm:";
+        strings_["enc_show_pass"] = "Show passphrase";
+        strings_["enc_min_len"] = "Use at least 8 characters.";
+        strings_["enc_mismatch"] = "The passphrases don't match.";
         strings_["enc_encrypting"] = "Encrypting wallet...";
         strings_["enc_wait"] = "Please wait, do not close the application.";
         strings_["enc_success"] = "Wallet encrypted successfully!";