feat: remove legacy OpenCode runtime

Cut product flows over to Coding/Pi and retain only the migration-owned v1 boundary. Promote supported native optional packages because electron-builder omitted pnpm transitive optional closure from the packaged ASAR.

tests/unit/branding-copy.test.ts

@@ -10,9 +10,9 @@ const displayCopyFiles = [
   'electron/main/menu.ts',
   'electron/main/tray.ts',
   'src/App.tsx',
-  'src/pages/Chat/OpencodeChatPanel.tsx',
+  'src/pages/Chat/CodingChatPanel.tsx',
   'src/pages/Login/index.tsx',
-  'src/pages/Models/OpencodeRuntimePanel.tsx',
+  'src/pages/Models/index.tsx',
   'src/pages/Makelore/index.tsx',
 ];
 
@@ -61,7 +61,7 @@ describe('GUI branding copy', () => {
     expect(offenders).toEqual([]);
   });
 
-  it('does not expose opencode in localized UI strings', () => {
+  it('does not expose the retired runtime brand in localized UI strings', () => {
     const localeDir = join(process.cwd(), 'src', 'i18n', 'locales');
     const offenders = localeJsonFiles(localeDir).flatMap((file) => {
       const json = JSON.parse(readFileSync(file, 'utf8')) as unknown;