Remove conditional from Azure login step in deployment workflow

[Copilot]

This PR simplifies the Azure deployment workflow by consolidating the authentication to a single, unconditional login step using Federated Credentials.

Changes Made

• Removed conditional if: ${{ env.AZURE_CLIENT_ID != '' }} from the Federated Credentials login step
• Removed entire "Log in with Azure (Client Credentials)" step that used if: ${{ env.AZURE_CREDENTIALS != '' }}
• Removed unused AZURE_CREDENTIALS environment variable from the job

Before

The workflow had two conditional login steps:

- name: Log in with Azure (Federated Credentials)
  if: ${{ env.AZURE_CLIENT_ID != '' }}
  # ... federated credentials login

- name: Log in with Azure (Client Credentials)
  if: ${{ env.AZURE_CREDENTIALS != '' }}
  # ... client credentials login

After

The workflow now has a single, unconditional login step:

- 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 and reduces complexity
• Eliminates potential failure points from conditional logic
• Ensures consistent authentication method across all runs
• Follows current best practices for Azure authentication in GitHub Actions
• Removes dependency on legacy client credentials approach

Fixes #96.

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