[Issue] azd provision lacks actionable guidance for Cognitive Services RequestConflict

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**Output from `azd version`**

```text
azd version 1.29.0 (commit fc06de978b9e9dc98a50ebb601a18b0f9f24071a) (stable)
```

**Describe the bug**

When a Bicep template contains multiple sibling `Microsoft.CognitiveServices/accounts/deployments` resources under the same Cognitive Services/Azure AI Services account, ARM schedules those independent children concurrently. The `Microsoft.CognitiveServices` resource provider rejects the concurrent writes with `RequestConflict` because another operation is already running against the parent account.

The underlying concurrency restriction belongs to the resource provider, not azd. However, `azd provision` currently reports the deployment failure without actionable guidance that these child resources must be serialized. An azd error suggestion for this known provider response, and serialization in any azd-generated Azure AI model infrastructure, would make the failure diagnosable.

**To Reproduce**

1. Declare one `Microsoft.CognitiveServices/accounts` resource with `kind: 'AIServices'`.
2. Declare two or more `Microsoft.CognitiveServices/accounts/deployments` child resources with the account as `parent`, but no dependencies between the sibling deployments.
3. Run `azd provision --no-prompt`.
4. Observe that one model deployment may succeed while the concurrent siblings fail with:

```text
Code: RequestConflict
Message: Another operation is being performed on the parent resource ... Microsoft.CognitiveServices/accounts/. Please try again later.
```

5. Add an explicit `dependsOn` chain between the model deployments and run `azd provision` again.

We verified this with five model deployments. Without sibling dependencies, four failed with `RequestConflict` after roughly 0.7 seconds. With the dependency chain restored, all five model deployments and the complete provision succeeded.

**Expected behavior**

When azd encounters this known `Microsoft.CognitiveServices` parent-resource conflict, it should provide an actionable suggestion such as:

> Cognitive Services does not accept concurrent writes to deployment children of the same account. Serialize sibling model deployments with explicit Bicep `dependsOn` relationships and retry.

Any azd templates or generated infrastructure that create multiple model deployments under one account should also serialize those resources.

**Environment**

- OS: Linux
- azd: 1.29.0 stable
- Infrastructure: Bicep
- Resource type: `Microsoft.CognitiveServices/accounts/deployments@2026-05-01`
- Parent account kind: `AIServices`

**Additional context**

The tested mitigation is documented in Azure/azure-sdk-tools#16357:

https://github.com/Azure/azure-sdk-tools/blob/qiaozha/sdk-ai-bots-deployment/tools/sdk-ai-bots/deployment/infra/modules/qaBotAgent/component.bicep

A `parent` declaration creates an account-before-child dependency, but it does not serialize independent sibling child resources. Explicit sibling dependencies are still required for this provider.

Start by reproducing the failure with `azd provision --no-prompt` using sibling `Microsoft.CognitiveServices/accounts/deployments` resources, then inspect azd's handling of the `Microsoft.CognitiveServices` `RequestConflict` response. Use the referenced `component.bicep` example as a serialization reference; done means the error provides actionable guidance and applicable generated infrastructure serializes sibling deployments.

Written by the indexing model from the issue text.