feat(FN-3227): add startup model sync for opencode-go commands

- Add shared startup model sync helper and integrate it into dashboard, serve, and daemon command startup flows
- Introduce opencode-go model sync setting in core schema/types and expose it in dashboard settings UI
- Add CLI regression tests covering startup model sync behavior and command wiring
- Document the new startup model sync setting and related CLI behavior updates

Fusion-Task-Id: FN-3227

packages/core/src/settings-schema.ts

@@ -45,6 +45,7 @@ export const DEFAULT_GLOBAL_SETTINGS = {
   favoriteProviders: undefined,
   favoriteModels: undefined,
   openrouterModelSync: true,
+  opencodeGoModelSync: true,
   updateCheckEnabled: true,
   fnBinaryCheckEnabled: true,
   updateCheckFrequency: "daily",