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/host-events.test.ts

@@ -30,9 +30,9 @@ describe('host-events', () => {
 
     const { subscribeHostEvent } = await import('@/lib/host-events');
     const handler = vi.fn();
-    const unsubscribe = subscribeHostEvent('opencode:status', handler);
+    const unsubscribe = subscribeHostEvent('auth:session-changed', handler);
 
-    expect(onMock).toHaveBeenCalledWith('opencode:status', expect.any(Function));
+    expect(onMock).toHaveBeenCalledWith('auth:session-changed', expect.any(Function));
     expect(createHostEventSourceMock).not.toHaveBeenCalled();
 
     captured[0]({ state: 'running' });