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.

src/lib/host-events.ts

@@ -3,8 +3,6 @@ import { createHostEventSource } from './host-api';
 let eventSource: EventSource | null = null;
 
 const HOST_EVENT_TO_IPC_CHANNEL: Record<string, string> = {
-  'opencode:status': 'opencode:status',
-  'opencode:stderr': 'opencode:stderr',
   'oauth:code': 'oauth:code',
   'oauth:success': 'oauth:success',
   'oauth:error': 'oauth:error',