@google-cloud/secret-manager generated protos expose protobufjs/minimal to bundlers under pnpm

### Package

`@google-cloud/secret-manager`

### Version

Observed with:

- `@google-cloud/secret-manager@6.1.2`
- `google-gax@5.0.6`
- `pnpm@10.33.2`
- `next@15.5.15` / webpack production build
- Vercel build environment

### What happened?

A Next.js/Vercel production build failed while bundling an API route that imports Secret Manager:

```text
Failed to compile.
../../node_modules/.pnpm/@google-cloud+secret-manager@6.1.2/node_modules/@google-cloud/secret-manager/build/protos/protos.js
Module not found: Can't resolve 'protobufjs/minimal'

Import trace for requested module:
../../node_modules/.pnpm/@google-cloud+secret-manager@6.1.2/node_modules/@google-cloud/secret-manager/build/src/index.js
./src/lib/jwt-keys.ts
./src/app/api/internal/mint-token/route.ts
```

The generated `build/protos/protos.js` file contains both an AMD dependency on `protobufjs/minimal` and a CommonJS path through `google-gax`:

```js
if (typeof define === 'function' && define.amd)
define(["protobufjs/minimal"], factory);
else if (typeof require === 'function' && typeof module === 'object' && module && module.exports)
module.exports = factory(require("google-gax/build/src/protobuf").protobufMinimal);
```

`google-gax/build/src/protobuf.js` does correctly re-export `protobufjs/minimal`, and `google-gax@5.0.6` declares `protobufjs`:

```text
google-gax@5.0.6 -> protobufjs ^7.5.3
```

However, under pnpm's isolated node_modules layout, `@google-cloud/secret-manager` can see `google-gax`, but it does not directly see `protobufjs`. Webpack/Next appears to statically process the AMD dependency string in `protos.js` and tries to resolve `protobufjs/minimal` from the Secret Manager proto module itself, instead of relying only on the CommonJS `google-gax/build/src/protobuf` path.

### Expected behavior

A server-side Next.js/webpack build should not need the application package to add `protobufjs` explicitly just to bundle `@google-cloud/secret-manager`, since Secret Manager's runtime CommonJS path goes through `google-gax`, and `google-gax` owns the `protobufjs` dependency.

Ideally the generated Secret Manager proto output would not expose a direct `protobufjs/minimal` dependency to bundlers unless `@google-cloud/secret-manager` itself declares that dependency.

### Workaround

Adding `protobufjs` explicitly to the consuming package fixes the Vercel/Next build:

```json
{
"dependencies": {
"@google-cloud/secret-manager": "^6.1.2",
"protobufjs": "^7.5.5"
}
}
```

In our pnpm workspace, this made `protobufjs/minimal` visible to the application bundle and the auth service build passed again.

### Why I think this is an upstream packaging/generation issue

The package metadata currently looks like this:

```text
@google-cloud/secret-manager@6.1.2
dependencies:
google-gax: ^5.0.0

google-gax@5.0.6
dependencies:
protobufjs: ^7.5.3
@grpc/proto-loader: ^0.8.0
proto3-json-serializer: ^3.0.0
```

That dependency graph is fine for Node's CommonJS runtime path, but the generated `define(["protobufjs/minimal"], factory)` branch creates a direct-looking static dependency from the Secret Manager proto file. Bundlers can try to resolve that dependency from `@google-cloud/secret-manager`, where pnpm has not linked `protobufjs` because Secret Manager does not declare it directly.

Would you consider either removing/altering the AMD dependency emitted in generated proto files, or declaring `protobufjs` directly from packages whose generated output references `protobufjs/minimal`?