[codex] Replace mpv fullscreen toggle with launch mode config (#48)

Co-authored-by: bee <autumn@skerritt.blog>

src/shared/mpv-launch-mode.test.ts

@@ -0,0 +1,15 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { buildMpvLaunchModeArgs, parseMpvLaunchMode } from './mpv-launch-mode';
+
+test('parseMpvLaunchMode normalizes valid string values', () => {
+  assert.equal(parseMpvLaunchMode(' fullscreen '), 'fullscreen');
+  assert.equal(parseMpvLaunchMode('MAXIMIZED'), 'maximized');
+  assert.equal(parseMpvLaunchMode('normal'), 'normal');
+});
+
+test('buildMpvLaunchModeArgs returns the expected mpv flags', () => {
+  assert.deepEqual(buildMpvLaunchModeArgs('normal'), []);
+  assert.deepEqual(buildMpvLaunchModeArgs('maximized'), ['--window-maximized=yes']);
+  assert.deepEqual(buildMpvLaunchModeArgs('fullscreen'), ['--fullscreen']);
+});