Remove conditional Azure login steps and simplify to single Federated Credentials auth

[Copilot]

Simplified Azure authentication in deployment workflows by removing conditionals and consolidating to a single login step using Federated Credentials.

Changes Made

azure-dev.yaml:

• Removed if: ${{ env.AZURE_CLIENT_ID != '' }} conditional from the Azure login step
• Login step now executes unconditionally using Federated Credentials

evaluate.yaml:

• Removed if: ${{ env.AZURE_CLIENT_ID != '' }} conditional from the azd login step
• Removed the azure/login@v2 action that used Client Credentials
• Removed the dependent "Set az account" step
• Now has a single, unconditional login step using Federated Credentials

Both workflow files now have exactly the login format specified in the issue:

- name: Log in with Azure (Federated Credentials)
  run: |
    azd auth login `
      --client-id "$Env:AZURE_CLIENT_ID" `
      --federated-credential-provider "github" `
      --tenant-id "$Env:AZURE_TENANT_ID"
  shell: pwsh

Benefits

• Simplifies workflow logic by removing conditionals
• Reduces complexity and potential failure points
• Ensures consistent authentication method across workflows
• Follows current best practices for Azure authentication in GitHub Actions

Fixes #239.

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