feat(settings): split import into separate key + viewing-key buttons

Backup & Data now has two distinct import actions instead of one
auto-detecting dialog:

- "Import Key" imports a spending key (transparent WIF or shielded
  z-spending key) with the strong "grants access to funds" warning.
- "Import Viewing Key" imports a watch-only shielded viewing key
  (zxviews…) with a milder eye/watch-only note and an optional
  "scan from block height" field — z_importviewingkey accepts a start
  height, so watching a recent address needn't rescan the whole chain.

The shared Material dialog (renderImportKeyDialog) branches on
import_view_mode_: title, warning tone, field label, the live type
indicator, and the recognition guard. A key valid for the *other*
button (e.g. a spending key pasted into the viewing-key dialog) now
shows a redirect hint rather than a generic "unrecognized" error.

importPrivateKey gains a startHeight arg, appended to the shielded
import RPCs (z_importviewingkey / z_importkey) and ignored for
transparent WIF (importprivkey has no start-height param). The
scan-height buffer is wiped on open/close alongside the key buffer.

i18n: 9 new keys (button label + tooltip, viewing title/note/field,
scan label/hint, two wrong-type redirect hints) with translations for
all 8 languages; CJK subset rebuilt (+1 glyph). A modal-import-viewkey
sweep surface is added for the viewing-mode dialog.

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

src/ui/pages/settings_page.cpp

@@ -1349,12 +1349,14 @@ void RenderSettingsPage(App* app) {
             float naturalW = 0;
             for (int i = 0; i < 5; i++)
                 naturalW += ImGui::CalcTextSize(r1[i]).x + btnPadX;
+            float impViewW = ImGui::CalcTextSize(TR("settings_import_viewkey")).x + btnPadX;
+            naturalW += impViewW;   // the extra "Import viewing key" button (rendered after Import key)
             float wizW = showFullNodeLifecycleActions ? ImGui::CalcTextSize(wizLabel).x + btnPadX : 0.0f;
             float bsW = showFullNodeLifecycleActions ? ImGui::CalcTextSize(bsLabel).x + btnPadX : 0.0f;
             // Full-node-only "Seed phrase" + "Migrate to seed" buttons trail the Backup button.
             float seedW = showFullNodeLifecycleActions ? ImGui::CalcTextSize(TR("seed_backup_button")).x + btnPadX : 0.0f;
             float migrateW = showFullNodeLifecycleActions ? ImGui::CalcTextSize(TR("seed_migrate_button")).x + btnPadX : 0.0f;
-            float totalW = naturalW + sp * 5;
+            float totalW = naturalW + sp * 6;   // 6 base buttons (incl. Import viewing key)
             if (showFullNodeLifecycleActions) totalW += wizW + bsW + seedW + migrateW + sp * 4;
 
             float scale = (totalW > contentW) ? contentW / totalW : 1.0f;
@@ -1364,6 +1366,11 @@ void RenderSettingsPage(App* app) {
             if (TactileButton(r1[0], ImVec2(0, 0), btnFont))
                 app->showImportKeyDialog();
             if (ImGui::IsItemHovered()) material::Tooltip("%s", t1[0]);
+            // Watch-only shielded viewing-key import (separate button — different key type + scan-height).
+            ImGui::SameLine(0, scaledSp);
+            if (TactileButton(TR("settings_import_viewkey"), ImVec2(0, 0), btnFont))
+                app->showImportViewingKeyDialog();
+            if (ImGui::IsItemHovered()) material::Tooltip("%s", TR("tt_import_viewkey"));
             ImGui::SameLine(0, scaledSp);
             if (TactileButton(r1[1], ImVec2(0, 0), btnFont))
                 app->showExportKeyDialog();