Fix PushChanges return value handling for direct commits

[Copilot]

❔What, Why & How

PushChanges only returned a value on the PR creation path, leaving $prUrl null for direct commits. This resulted in misleading output: "PR URL: " with no value.

Changes:

• Return empty string when DirectCommit is true
• Conditionally display PR URL in notice message only when non-empty

# Before
Write-Host "::notice::Deployed to $repo branch $branch. PR URL: $prUrl"
# Output for direct commits: "Deployed to repo branch main. PR URL: "

# After
if ($prUrl) {
    Write-Host "::notice::Deployed to $repo branch $branch. PR URL: $prUrl"
} else {
    Write-Host "::notice::Deployed to $repo branch $branch"
}
# Output for direct commits: "Deployed to repo branch main"

✅ Checklist

• Add tests (E2E, unit tests)
• Update RELEASENOTES.md
• Update documentation (e.g. for new settings or scenarios)
• Add telemetry

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.