feat(theme-studio): prev/next arrows to step the view dropdown

I added left and right arrow buttons flanking the view dropdown. They step the selection to the previous or next item and re-render the faces table and preview, so you can walk the list without reopening the dropdown. A pure stepViewIndex helper clamps the index to the option range, no wrap. stepView sets the selection and calls onViewChange.

1 files changed, 18 insertions, 1 deletions

diff --git a/scripts/theme-studio/test-app-core.mjs b/scripts/theme-studio/test-app-core.mjs
index 20f3d573..8f62ae55 100644
--- a/scripts/theme-studio/test-app-core.mjs
+++ b/scripts/theme-studio/test-app-core.mjs
@@ -9,7 +9,7 @@ import { fileURLToPath } from 'node:url';
 import {
   nameToHex, normalizePkgFace, buildPkgmap, packagesForExport, mergePackagesInto, effResolve, resolveSyntaxFg, resolveUiAttr, dropdownRowTextColor, paletteOptionList, spanNeighborHex, slugify,
   clearPalettePlan, deletePaletteColumnPlan, groundColumnMembersFromPalette, areAllLocked, lockToggleLabel, toggleLockSet,
-  galleryModel, appViewKeysSorted, faceBoxNonDefaults,
+  galleryModel, appViewKeysSorted, faceBoxNonDefaults, stepViewIndex,
 } from './app-core.js';
 import { planPaletteGenerator, entriesForGeneratedColumn } from './palette-generator-core.js';
 import { oklch2hex, deltaE } from './colormath.js';
@@ -878,3 +878,20 @@ test('faceBoxNonDefaults: nullish inputs flag nothing', () => {
   assert.deepEqual(faceBoxNonDefaults(null, null),
     { fg: false, bg: false, style: false, inherit: false, height: false, box: false });
 });
+
+// stepViewIndex: the prev/next arrows step the view-dropdown selection, clamped
+// to the option range (no wrap).
+test('stepViewIndex: steps forward and back within range', () => {
+  assert.equal(stepViewIndex(2, 5, 1), 3);
+  assert.equal(stepViewIndex(2, 5, -1), 1);
+});
+test('stepViewIndex: clamps at both ends, no wrap', () => {
+  assert.equal(stepViewIndex(0, 5, -1), 0);
+  assert.equal(stepViewIndex(4, 5, 1), 4);
+});
+test('stepViewIndex: a single option or empty list stays put', () => {
+  assert.equal(stepViewIndex(0, 1, 1), 0);
+  assert.equal(stepViewIndex(0, 1, -1), 0);
+  assert.equal(stepViewIndex(3, 0, -1), 3);
+  assert.equal(stepViewIndex(0, 0, 1), 0);
+});