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.

electron/api/host-api-transport.ts

@@ -7,7 +7,6 @@ export function shouldUseLoopbackHostApi(path: string, method = 'GET'): boolean
   const normalizedMethod = method.toUpperCase();
   const pathname = path.split('?', 1)[0] || path;
   if (pathname === '/api/events'
-    || pathname === '/api/opencode/events'
     || pathname === '/api/coding/events') return true;
   if (pathname === '/api/coding/attachments'
     || pathname.startsWith('/api/coding/attachments/')) return true;