Generate dry-run package plans for desktop-win builds

[RasputinKaiser]

desktop-win build currently logs the Windows distribution target and returns an output path, but dry-run builds do not leave an inspectable package plan for MSIX/MSI outputs. That makes it harder to validate Windows packaging from non-Windows machines and harder for callers to see the expected makeappx/WiX/signtool steps.\n\nProposed fix:\n- emit a dry-run Windows package-plan JSON artifact under the target outDir\n- include MSIX/MSI artifact paths for msstore, msi, or both distributions\n- include planned makeappx, WiX, and signtool commands without executing Windows-only tooling\n- flag the missing signing certificate thumbprint as follow-up data in the plan\n- cover the plan with focused desktop-win target tests

[Robertg761]

Implemented in PR #181: #181

Summary:

• dry-run desktop-win builds now write windows-package-plan.json
• plan includes MSIX/MSI artifact paths for msstore/msi/both distributions
• plan includes makeappx, WiX, and signtool argv commands without executing Windows-only tooling
• missing signingCertThumbprint is flagged as follow-up data

Verification:

• pnpm exec vitest run packages/targets/desktop-win/src/index.test.ts
• pnpm --filter @profullstack/sh1pt-target-desktop-win typecheck
• pnpm --filter @profullstack/sh1pt typecheck
• git diff --check