`vp migrate` silently drops custom lint rules when a `jsPlugin`'s namespace can't be derived

### Describe the bug

When `vp migrate` merges `.oxlintrc.json` into `vite.config.ts`, it drops all rules whose namespace it can't match to a plugin.

For a local jsPlugin like `./lint/kumo.js`, the plugin's real namespace (`kumo`, from its `meta.name`) is never derived from the path, so every `kumo/*` rule is removed from the merged config.

This happens silently for rules while dropped plugins produce a warning.

#### Solution approach

We could resolve the real namespace (import the plugin and read meta.name) which is exactly what oxlint does at lint time.

### Reproduction

https://github.com/cloudflare/kumo/commit/2a463f7f260f5a3c4523099600fe65b4764acff4

### Steps to reproduce

1. Try migrating this app via `vp migrate`
2. See the rules missing

### System Info

```shell
Source .node-version
Source Path /Users/alichter/Programming/kumo/.node-version
Project Root /Users/alichter/Programming/kumo

Tool Paths:
node /Users/alichter/.vite-plus/js_runtime/node/24.12.0/bin/node
npm /Users/alichter/.vite-plus/js_runtime/node/24.12.0/bin/npm
npx /Users/alichter/.vite-plus/js_runtime/node/24.12.0/bin/npx

Package Manager:
Name pnpm
Version 10.22.0
Source packageManager
Source Path /Users/alichter/Programming/kumo/package.json
Project Root /Users/alichter/Programming/kumo
Bin Path /Users/alichter/.vite-plus/package_manager/pnpm/10.22.0/pnpm/bin/pnpm
```

### Used Package Manager

pnpm

### Logs

```shell

```

### Validations

- [x] Read the [Contributing Guidelines](https://github.com/voidzero-dev/vite-plus/blob/main/CONTRIBUTING.md).
- [x] Check that there isn't [already an issue](https://github.com/voidzero-dev/vite-plus/issues) for the same bug.
- [x] Confirm this is a Vite+ issue and not an upstream issue (Vite, Vitest, tsdown, Rolldown, or Oxc).
- [x] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example).

`.oxlintrc.json` を `vite.config.ts` にマージするエントリポイント `vp migrate` から始め、ローカルの `jsPlugin` namespace がどのように照合されるかを追跡します。リンクされた Kumo の commit で再現し、`./lint/kumo.js` プラグインの `meta.name` を調べます。その `kumo/*` ルールが migration 後も残り、削除されたプラグインについても結果を引き続き観測できれば完了です。

索引モデルが issue の本文から書いたものです。