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

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

launcher/config-domain-parsers.test.ts

@@ -2,6 +2,7 @@ import test from 'node:test';
 import assert from 'node:assert/strict';
 import { parseLauncherYoutubeSubgenConfig } from './config/youtube-subgen-config.js';
 import { parseLauncherJellyfinConfig } from './config/jellyfin-config.js';
+import { parseLauncherMpvConfig } from './config/mpv-config.js';
 import { readExternalYomitanProfilePath } from './config.js';
 import {
   getPluginConfigCandidates,
@@ -80,6 +81,27 @@ test('parseLauncherJellyfinConfig omits legacy token and user id fields', () =>
   assert.equal('userId' in parsed, false);
 });
 
+test('parseLauncherMpvConfig reads launch mode preference', () => {
+  const parsed = parseLauncherMpvConfig({
+    mpv: {
+      launchMode: ' maximized ',
+      executablePath: 'ignored-here',
+    },
+  });
+
+  assert.equal(parsed.launchMode, 'maximized');
+});
+
+test('parseLauncherMpvConfig ignores invalid launch mode values', () => {
+  const parsed = parseLauncherMpvConfig({
+    mpv: {
+      launchMode: 'wide',
+    },
+  });
+
+  assert.equal(parsed.launchMode, undefined);
+});
+
 test('parsePluginRuntimeConfigContent reads socket path and startup gate options', () => {
   const parsed = parsePluginRuntimeConfigContent(`
 # comment