Support prompt voice telephony bindings

[JianW (v1212)]

Summary

• Adds azure.yaml support for Foundry-side telephony bindings on prompt voice agents.
• Keeps the user experience nearly unchanged: users still run azd ai agent init, azd provision, azd deploy, and azd down; no new command is introduced.
• Limits telephony binding support to kind: prompt-voice; other agent types reject telephony configuration.

What changes for users

Users can optionally add phone-number bindings to an existing prompt voice agent service:

services:
  support-voice:
    host: azure.ai.agent
    kind: prompt-voice
    name: support-voice
    model:
      id: gpt-realtime
    telephony:
      bindings:
        - provider: acs
          identifier: "28:orgid:<resource-account-object-id>"
          connection: telephony-acs
        - provider: twilio
          identifier: "+14255550123"
          connection: telephony-twilio

Then they continue to use the normal lifecycle:

azd provision
azd deploy support-voice

Scope

• This PR only creates Foundry-side telephony bindings after a prompt voice agent deploy succeeds.
• It does not purchase phone numbers, create Teams/TPE resources, create Twilio numbers, bootstrap Event Grid auth apps, or automate cross-tenant/admin telephony setup.
• Provider-side resources and project connections are prerequisites provided by the user/admin.
• agent_version and arbitrary provider_config are intentionally not exposed because the current service contract does not support version-pinned bindings and unknown provider config fields are ignored.
• This is a draft while the service team confirms the final telephony binding API contract, API version, and provider paths.

Validation

• provider must be acs or twilio.
• identifier and connection are required.
• ACS identifiers support 28:orgid:<guid> for TPE or 4:+<E.164> for ACS-purchased numbers.
• Twilio identifiers use +<E.164>.
• telephony on non-prompt-voice services is rejected unless an explicit AGENT_DEFINITION_PATH override is routing the deploy to a different agent definition.

Implementation

• Adds prompt voice telephony YAML models, schema, and inline azure.yaml round-trip support.
• Adds telephony binding API models and agent-scoped create/get operations.
• Runs binding creation after successful prompt voice deploy and agent version validation.
• Existing bindings are treated as create-only: matching bindings are accepted; drift is reported as an error rather than silently ignored.
• Adds tests for validation, round-trip, API request path/body, drift detection, and prompt-voice-only detection.

How to test

1. Prepare or reuse a prompt voice azd project.
2. Prepare provider-side telephony resources and a Foundry project connection (telephony-acs or telephony-twilio).
3. Add telephony.bindings[] to the prompt voice service in azure.yaml.
4. Run azd deploy <voice-service>.
5. Verify the binding by calling the service telephony binding GET/list API or by placing an inbound test call through the configured provider.

Validation run

• go test ./... -count=1
• go build ./...
• cspell lint 'extensions/**/*.go' 'extensions/**/*.md' --config ./.vscode/cspell.yaml --no-progress

Fixes #9803

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