`skaffold apply` rejects deploy flags when dependency config creates implicit deployer

## Description

When a skaffold config uses `requires` to import a dependency config that only provides a `resourceSelector`, `skaffold apply` rejects any `deploy.kubectl.flags` with:

```
creating runner: creating deployer: conflicting sets of kubectl deploy flags not supported in `skaffold apply` (flag: --server-side)
```

The dependency config has no `deploy` section — it only defines a `resourceSelector`. Skaffold creates an implicit (empty) deployer for it, and `skaffold apply` treats the parent's deploy flags and the dependency's implicit deployer as "conflicting sets."

`skaffold dev` and `skaffold deploy` work fine with the same configuration — only `skaffold apply` rejects it.

## Reproduction

**Dependency config** (`dependency.yaml`):
```yaml
apiVersion: skaffold/v4beta2
kind: Config
metadata:
name: "MyResourceSelector"
resourceSelector:
allow:
- groupKind: "MyResource.example.com"
image: [".*"]
```

**Parent config** (`skaffold.yaml`):
```yaml
apiVersion: skaffold/v4beta12
kind: Config
requires:
- configs: ["MyResourceSelector"]
path: dependency.yaml
build:
artifacts:
- image: my-image
manifests:
kustomize:
paths:
- ./k8s/
deploy:
kubectl:
flags:
apply:
- --server-side
```

```
$ skaffold apply --status-check=false --interactive=false \
-f skaffold.yaml rendered-manifest.yaml
creating runner: creating deployer: conflicting sets of kubectl deploy flags \
not supported in `skaffold apply` (flag: --server-side)
```

Moving `deploy.kubectl.flags` into a profile instead of the top-level config does not help — `skaffold apply` still rejects it.

## Workaround

Inline the `resourceSelector` directly into the parent config and remove the `requires` section.

## Expected behavior

`skaffold apply` should not treat an implicit (empty) deployer from a dependency config as a conflicting set of deploy flags. Dependency configs that only provide non-deploy settings like `resourceSelector` should not interfere with the parent's deploy configuration.

## Environment

- Skaffold version: v2.18.3, v2.19.0
- OS: Linux
- Kubernetes: v1.35.x