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/preload/index.ts

@@ -13,11 +13,6 @@ const validInvokeChannels = [
   'hostapi:fetch',
   'hostapi:token',
   'hostapi:base-url',
-  'opencode:status',
-  'opencode:start',
-  'opencode:stop',
-  'opencode:restart',
-  'opencode:health',
   'lifecycle:activity',
   'lifecycle:lease',
   'shell:openExternal',
@@ -71,8 +66,6 @@ const validInvokeChannels = [
 
 const validEventChannels = [
   'navigate',
-  'opencode:status',
-  'opencode:stderr',
   'update:status-changed',
   'update:checking',
   'update:available',