ci: add static and Windows regression checks

[wasim-builds]

Resolves #20.

Adds GitHub Actions coverage for checks that do not require Codex.app:

• Bash syntax, Node.js syntax, runtime safety, source-encoding, and cross-platform version checks.
• Portable macOS and Windows Node.js regressions plus payload validation on Ubuntu.
• The complete Windows regression suite on Windows PowerShell 5.1 and PowerShell 7 with Node.js 22.

The first real Windows run exposed that PowerShell 5.1 parsed non-ASCII UTF-8 source through the local ANSI code page. The three PowerShell files containing Chinese text are now explicitly UTF-8 with BOM, and CI prevents future non-ASCII PowerShell 5.1 sources from losing that marker.

Maintainer update: rebased onto current main, corrected stale repository paths, and retained the original contributor as commit author.

[Copilot]

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[Fei-Away]

Maintainer update applied: rebased this contribution onto current main, fixed the stale ./assets and root VERSION paths, switched validation to Node.js 22, and added the complete Windows test suite on both Windows PowerShell 5.1 and PowerShell 7.

Local validation passed for YAML parsing, shell/Node syntax, runtime safety assertions, version consistency, and git diff --check. The original commit author remains @wasim-builds. Waiting for the new Actions runs before merge.

[Fei-Away]

Maintainer fixes validated locally. Approving pending the Windows and static Actions results.

[Fei-Away]

The first Windows PowerShell 5.1 run did its job and exposed a real source-encoding failure: non-ASCII UTF-8 .ps1 files without a BOM were parsed through the runner ANSI code page. I fixed the three affected PowerShell files (theme-windows.ps1, tray-dream-skin.ps1, and run-tests.ps1) and added a static guard so future non-ASCII PS 5.1 source must retain UTF-8 BOM.

The workflow now also runs both portable Node test suites and payload checks. Local Node regressions (8/8), payload validation, PowerShell 7 parsing, YAML parsing, and git diff --check all pass. Re-running both Windows shells independently now.

[wasim-builds]

Pushed a follow-up fix to wasim-builds:ci-workflow for the failing Windows (Windows PowerShell 5.1) check.

Root cause: Invoke-DreamSkinNative piped native output through ForEach-Object before reading $LASTEXITCODE, which can lose the native process exit code in PowerShell 5.1 pipelines.

Fix: capture native output first, snapshot $LASTEXITCODE immediately, then format output lines. This preserves the real native exit code while still handling stderr safely under ErrorActionPreference='Stop'.

[Fei-Away]

All required checks are green on the current head: portable static/Node regressions, Windows PowerShell 5.1, and PowerShell 7. The contributor follow-up correctly captures $LASTEXITCODE before PowerShell 5.1 stringifies native stderr output. Approved for squash merge.

[Fei-Away]

Final validation passed on the current head: Static checks ✅, Windows PowerShell 5.1 ✅, PowerShell 7 ✅. Thank you @wasim-builds for following the first Windows failure and contributing the native exit-code correction directly.