Consolidate XAML server publish and payload validation

Is your feature request related to a problem? Please describe.

PR #50 introduced self-contained XAML server delivery. The ARM64 CI job currently repeats the canonical publish commands, and required runtime payload filenames are repeated in the bundle helper, VSIX validator, and delivery tests. These copies can drift as the runtime payload changes.

Describe the solution you'd like

Add a single-RID option to the canonical server bundle helper and move the RID/required-file definitions into one shared manifest consumable by Node and PowerShell validation paths. Use the helper from the ARM64 smoke job.

Additional context

This is follow-up refactoring from the final PR review. Current delivery and validation are functionally covered and passing.

Start by locating the canonical server bundle helper, the ARM64 smoke job, and the bundle helper, VSIX validator, and delivery tests mentioned in the issue. Trace how each currently defines the RID and required payload files, then identify how a shared manifest can be consumed by both Node and PowerShell paths. Done means the ARM64 job uses the helper and validation definitions have one source of truth without changing the passing delivery behavior.