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/pages/Chat/message-utils.ts

@@ -1,6 +1,6 @@
 /**
  * Message content extraction helpers
- * Handles the various message content formats returned by opencode.
+ * Handles the various message content formats returned by coding providers.
  */
 import type { RawMessage, ContentBlock } from '@/types/chat';