feat(release): add Microsoft Store (MSIX) packaging

[EtienneLescot]

Summary

• Add an appx target to electron-builder alongside the existing NSIS installer, with the Microsoft Store package identity (EtienneLescot.OpenScreen) reserved in Partner Center and microphone/webcam capabilities declared
• Add a build:win:store npm script
• Add a build-windows-store CI job to build.yml that produces the .appx artifact on every tag build

Context

First step toward publishing OpenScreen on the Microsoft Store. NSIS remains the default/primary Windows distribution channel — this is purely additive. Store submission itself (Partner Center listing, screenshots, age rating) is handled outside this repo and is in progress separately.

Test plan

• Local build verified: npm run build:win:store produces a valid signed-for-testing .appx that installs and runs (screen/mic/webcam capture confirmed working from the packaged app)
• Manifest capabilities (runFullTrust, microphone, webcam) verified present in the built package
• CI job not yet exercised on a real tag push (will run automatically on the next release tag)

Summary by CodeRabbit

• New Features
  • Added support for building a Windows Store package.
  • Configured Microsoft Store identity, display information, supported capabilities, and languages.
  • Windows Store installer artifacts are now generated and available through the build process.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 780d0038-8c6b-4b25-a3e7-c34a1c637f76

📥 Commits

Reviewing files that changed from the base of the PR and between fe5e95b and 6cc398d.

📒 Files selected for processing (3)

• .github/workflows/build.yml
• electron-builder.json5
• package.json

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📝 Walkthrough

Walkthrough

Adds Windows Store AppX packaging metadata, a dedicated npm build script, and a GitHub Actions job that builds and uploads the resulting .appx artifact.

Changes

Windows Store packaging

Layer / File(s)	Summary
AppX packaging configuration electron-builder.json5, package.json	The AppX target defines Store identity, display metadata, capabilities, background color, and supported languages; build:win:store runs the Windows AppX build pipeline.
Windows Store CI artifact .github/workflows/build.yml	A build-windows-store job builds the AppX package without publishing and uploads it as openscreen-windows-store with 30-day retention.

Estimated code review effort: 2 (Simple) | ~10 minutes

Sequence Diagram(s)

sequenceDiagram
  participant GitHubActions
  participant NpmScript
  participant ElectronBuilder
  participant ArtifactStorage
  GitHubActions->>NpmScript: run build:win:store
  NpmScript->>ElectronBuilder: build Windows AppX target
  ElectronBuilder-->>GitHubActions: produce .appx package
  GitHubActions->>ArtifactStorage: upload openscreen-windows-store

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Suggested reviewers: siddharthvaddem

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description has a useful summary and testing notes, but it omits several required template sections like Related issue, Type of change, and Release impact.	Add the missing template sections: related issue, type of change, release impact, desktop impact, screenshots/video, and fuller testing details.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly matches the PR's main change: adding Microsoft Store packaging.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch claude/windows-appstore-deployment-ff9e27

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