[bug]: webhook list panics when a policy has no targets

## Description
`harbor webhook list` panics when Harbor returns a webhook policy with an empty `targets` array.

The list view indexes `webhook.Targets[0]` unconditionally, but the generated Harbor client model does not require `targets` to be present or non-empty.

## Steps to Reproduce
1. Run `harbor webhook list ` against a Harbor instance that returns a webhook policy with `targets: []`.
2. Observe the CLI panic in the webhook list view.

A minimal repro at code level is calling the list view with `&models.WebhookPolicy{}`.

## Expected Behavior
The command should render the webhook row and fall back to placeholders when target details are missing.

## Actual Behavior
The CLI panics with an index-out-of-range error while rendering the list.

## Environment
- OS: All
- Tool version: current `main`
- Other relevant details: the generated `WebhookPolicy` model treats `targets` as optional and its validator allows zero values.

## Additional Context
`cmd/harbor/root/webhook/edit.go` already guards `len(selectedWebhook.Targets) > 0`, so the codebase already assumes this shape can happen.