Python: Hosted Responses sample loses invoke_agent token telemetry with latest hosting stack

### Describe the bug

The basic Agent Framework Responses hosted-agent sample does not emit the Agent Framework `invoke_agent` span or token usage attributes when deployed with the latest unpinned `agent-framework-foundry-hosting` dependency stack.

Sample:
https://github.com/microsoft-foundry/foundry-samples/tree/main/samples/python/hosted-agents/agent-framework/responses/01-basic

After pinning `agent-framework-foundry-hosting==1.0.0b260730`, the Agent Framework `invoke_agent` span and token attributes are emitted again.

### Reproduction

1. Deploy the sample to Microsoft Foundry using the Responses protocol and a `gpt-5` deployment.
2. Because Foundry invokes the hosted endpoint with `store=true`, enable resilient tasks before host startup:

```python
from azure.ai.agentserver.core.tasks import set_resilient_tasks_enabled

set_resilient_tasks_enabled(True)
```

3. Invoke the deployed agent normally.
4. Inspect the correlated trace in Application Insights.

### Failing dependency resolution

The unpinned sample resolved to:

- `azure-ai-agentserver-core==2.1.0b2`
- `azure-ai-agentserver-responses==2.1.0b1`
- latest available `agent-framework-foundry-hosting`

Observed behavior:

- The request succeeds after resilient tasks are enabled.
- Only the platform `invoke_agent` span is present.
- The Agent Framework `invoke_agent` span is absent.
- No `gen_ai.usage.input_tokens` or `gen_ai.usage.output_tokens` attributes are available.
- Runtime log contains:

```text
WARNING agent_framework_foundry_hosting._responses: Content type 'usage' is not supported yet. This is usually safe to ignore.
```

### Working dependency resolution

Change only the hosting requirement:

```text
agent-framework-foundry-hosting==1.0.0b260730
```

This transitively resolves `azure-ai-agentserver-responses==1.0.0b9` while retaining `azure-ai-agentserver-core==2.1.0b2`.

Observed behavior for the same sample and request:

- The Agent Framework `invoke_agent` span is emitted.
- `gen_ai.usage.input_tokens`, `gen_ai.usage.output_tokens`, and `gen_ai.usage.reasoning.output_tokens` are populated.
- Example observed values: input `29`, output `160`, reasoning `128`.

The `Content type 'usage' is not supported yet` warning is still logged in the working configuration, so the warning alone does not explain the missing span. This appears to be a compatibility/regression issue involving the newer hosting/AgentServer Responses stack.

### Expected behavior

The current unpinned hosted-agent stack should emit the Agent Framework `invoke_agent` span with model token usage attributes for successful Responses invocations, matching the behavior of the older compatible stack.

### Additional context

Without `set_resilient_tasks_enabled(True)`, `store=true` requests fail earlier with:

```text
Resilient task subsystem missing in hosted environment
```

That execution issue is resolved by enabling resilient tasks; this report concerns the remaining missing Agent Framework span and token telemetry after successful execution.