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/coding-attachments-routes.test.ts

@@ -80,7 +80,6 @@ async function startAuthenticatedHostServer() {
   roots.push(root);
   const attachments = new CodingAttachmentStore(root, { createId: () => 'host-attachment-1' });
   const context = {
-    opencodeManager: { getStatus: () => ({ url: null }) },
     codingProducts: { attachments },
   } as unknown as HostApiContext;
   const server = startHostApiServer(context, 0);