ECR repository creation required even with CodeZip build type

### Problem
When deploying an agent with `"build": "CodeZip"`, the deployment process still attempts to create an ECR repository, causing failures when ECR permissions are restricted by SCPs or IAM policies.

### Expected Behavior
CodeZip builds should only:
- Package Python source code as a zip file
- Upload to S3 or AgentCore's managed storage
- Deploy directly to AgentCore Runtime

ECR should **not** be required for CodeZip builds. ECR is only needed for Container builds.

### Actual Behavior
Running `agentcore deploy` with CodeZip build type triggers:
```
Error: ECR Permission Denied - ecr:CreateRepository
```

This occurs even though the configuration explicitly uses CodeZip:

**agentcore.json:**
```json
{
"runtimes": [
{
"name": "agent",
"build": "CodeZip",
"entrypoint": "main.py",
"codeLocation": "app/agent/",
"runtimeVersion": "PYTHON_3_14"
}
]
}
```

### Impact
- Blocks deployment in AWS accounts with restrictive SCPs that deny ECR operations
- Requires unnecessary ECR permissions even when not using containers
- Forces users to either:
- Grant ECR permissions unnecessarily (security concern)
- Switch to accounts without SCP restrictions (not always possible)

### Workaround
Deploy to AWS accounts without ECR permission restrictions.

### Environment
- AgentCore CLI version: latest as of 2026-05-26
- Build type: CodeZip
- Runtime: Python 3.14
- Deployment target: AWS account with SCP blocking `ecr:CreateRepository`

### Expected Fix
CodeZip builds should not require any ECR operations or permissions.