pipedv1-exp quickstart: syncing legacy-style example apps fails with "no plugin specified"

What happened:
Following the v1.0.x quickstart with pipedv1-exp, registering an application from the examples repo (e.g. kubernetes/kustomize-local-base) and triggering a sync fails with:

Unable to plan the deployment (no plugin specified)

Environment:

• Setup: local kind cluster, control-plane + pipedv1-exp installed via the quickstart manifests (master branch)
• Application: kubernetes/kustomize-local-base from pipe-cd/examples, added via "PIPED v1 ADD FROM SUGGESTIONS"

What I expected to happen:
Either the deployment to sync successfully, or the quickstart docs to note that pipedv1-exp requires app.pipecd.yaml configs to declare a plugins field, and that legacy-style example configs in pipe-cd/examples don't yet include one for the v1 plugin flow.

How to reproduce it:

1. Follow docs-v1.0.x/quickstart with pipedv1-exp
2. Add any application from examples via "ADD FROM SUGGESTIONS"
3. Trigger SYNC from the console
4. Observe the deployment fails immediately with "no plugin specified"

Screenshot of the failure:

Start with docs-v1.0.x/quickstart and the app.pipecd.yaml files for the legacy-style applications in the pipe-cd/examples repository. Trace the PIPED v1 ADD FROM SUGGESTIONS flow through a sync and check how the missing plugins field leads to the reported error. Done means the quickstart example syncs successfully or clearly documents the required v1 plugin configuration.