feat(deploy): NetScript.Aspire.Packaging — .NET Aspire hosting integration (ATS-exported) for installer authoring

[rickylabs]

Part of #327.

Owner-ratified resolution of RFC fork OF-D (2026-07-17): no Deno-native combined-MSI path exists — deno desktop's pure-Rust MSI packages only the window bundle (per-machine, no adjacent sidecars) and its docs punt to WiX/NSIS/Inno for anything more. Ship the packaging layer as a first-class C# Aspire hosting integration instead:

• A NuGet (NetScript.Aspire.Packaging) annotated with ATS [AspireExport] attributes so the Aspire CLI generates a typed TypeScript SDK (JSON-RPC into the C# code at runtime) — consumable as decorators/publish-pipeline steps from the TS AppHost (aspire.dev "Multi-language integrations").
• v1 scope: MSI authoring over a staged combined artifact (window + sidecars + tools), signtool hook, uninstaller/shortcut registration. deb/rpm stays native-side.
• Consumed by feat(deploy): single-artifact packaging + release server + snapshot updater (substrate) #456 (single-artifact substrate) now and SD-3 (graph installers) later.

Acceptance:

• gate: TS AppHost pipeline step invokes the generated SDK and emits an installable MSI from a staged directory
• gate: EnableAspireIntegrationAnalyzers clean; ATS export surface documented
• gate: .NET dependency is build-machine-only (end users need nothing) — documented

Design source: PR #822 (rfc.md + plan.md rev 10, 9-cycle adversarial trail) in .llm/runs/rfc-single-deployment--orchestrator/.