Add selectable fullscreen orientation and an iPhone landscape overlay

frontend/fullscreen-orientation.test.js

@@ -0,0 +1,17 @@
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const { normalize, rotation, coordinates } = require('./fullscreen-orientation');
+test('orientation defaults and only rotates mismatched viewports', () => {
+  assert.equal(normalize('invalid'), 'auto');
+  assert.equal(rotation('auto', 390, 844), 0);
+  assert.equal(rotation('landscape', 390, 844), 90);
+  assert.equal(rotation('landscape', 844, 390), 0);
+  assert.equal(rotation('portrait', 844, 390), -90);
+});
+test('rotated touch coordinates preserve local seek and swipe axes', () => {
+  const rect = { left: 10, top: 20, right: 400, bottom: 864, width: 390, height: 844 };
+  assert.deepEqual(coordinates(400, 20, rect, 90), { x: 0, y: 0, width: 844, height: 390 });
+  assert.deepEqual(coordinates(10, 864, rect, 90), { x: 844, y: 390, width: 844, height: 390 });
+  assert.deepEqual(coordinates(10, 864, rect, -90), { x: 0, y: 0, width: 844, height: 390 });
+  assert.deepEqual(coordinates(205, 442, rect), { x: 195, y: 422, width: 390, height: 844 });
+});