Quota warning suggests wrong region variable for AI model deployment

# Describe the bug

During `azd up`, the model-quota preflight correctly reports that `gpt-5.4-mini` (`GlobalStandard`) has no available quota in `australiaeast`, but its remediation suggests:

```bash
azd env set AZURE_LOCATION
```

This repository separates the non-AI resource region (`AZURE_LOCATION`) from the Foundry/model region (`AZURE_AI_SERVICE_LOCATION`). Following the warning would move Container Apps, Functions, Storage, and database resources instead of changing only the AI deployment region.

# Expected behavior

The warning should suggest:

```bash
azd env set AZURE_AI_SERVICE_LOCATION
```

Alternatively, the message should distinguish the AI model location from the general infrastructure location.

# How does this bug make you feel?

The remediation is misleading because it changes the deployment topology for unrelated resources.

---

# Debugging information

## Steps to reproduce

1. Use the current `main` branch.
2. Select `australiaeast` for both `AZURE_LOCATION` and `AZURE_AI_SERVICE_LOCATION`.
3. Set `AZURE_GPT_MODEL_NAME` to `gpt-5.4-mini` and `AZURE_GPT_MODEL_VERSION` to `2026-03-17`.
4. Use the default `GlobalStandard` SKU and 50K TPM capacity.
5. Run `azd up` with a subscription that has zero available quota for that model in Australia East.
6. Observe the suggested `AZURE_LOCATION` command.

## Environment

- OS: Linux dev container
- azd: `1.29.0`
- Model: `gpt-5.4-mini`
- Version: `2026-03-17`
- SKU: `GlobalStandard`
- AI region: `australiaeast`
- Requested capacity: 50K TPM
- Available capacity: 0

## Logs

```text
(!) Warning: Insufficient quota for model "gpt-5.4-mini" (SKU: GlobalStandard) in australiaeast
Requested: 50 · Available: 0
Suggestion: No quota is available. Change your deployment location via azd env set AZURE_LOCATION or request a quota increase in the Azure portal.
```

# Tasks

_To be filled in by the engineer picking up the issue_

- [ ] Update the quota-warning remediation to reference the AI-specific location variable.
- [ ] Add coverage for templates with separate infrastructure and AI regions.

Start with the quota preflight and remediation exercised by `azd up`, then trace how `AZURE_LOCATION` and `AZURE_AI_SERVICE_LOCATION` are selected in the templates. Reproduce the no-quota case and add coverage for templates with separate infrastructure and AI regions; done means the warning changes only the AI deployment location.

Written by the indexing model from the issue text.