Register Microsoft.KeyVault provider before Key Vault creation

[Copilot]

Deployments fail with MissingSubscriptionRegistration when the subscription hasn't registered the Microsoft.KeyVault resource provider.

• Added _register_keyvault_provider() to PrerequisitesRoutes — runs az provider register --namespace Microsoft.KeyVault --wait before keyvault creation
• Called in both deploy() and ensure_keyvault_ready() paths, gating _create_keyvault()
• On failure, aborts early with a provider_registration step in the response

async def _register_keyvault_provider(self, steps: list[dict]) -> bool:
    ok, msg = await run_sync(
        self._az.ok,
        "provider", "register", "--namespace", "Microsoft.KeyVault", "--wait",
    )
    steps.append({
        "step": "provider_registration",
        "status": "ok" if ok else "failed",
        "detail": "Microsoft.KeyVault registered" if ok else (msg or "Unknown error"),
    })
    return ok

Original prompt

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This section details on the original issue you should resolve

<issue_title>MissingSubscriptionRegistration issue</issue_title>
<issue_description>Exception Details:\t(MissingSubscriptionRegistration) The subscription is not registered to use namespace 'Microsoft.KeyVault'.</issue_description>

<agent_instructions>please ensure that keyvault registration is done as part of deployment option</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes MissingSubscriptionRegistration issue #1

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