Electron App: Cross-platform packaging & CI

[jongio]

Overview

electron-builder configuration for packaging on all platforms with CI/CD.

Acceptance Criteria

• Windows: NSIS installer (x64, arm64), portable zip, auto-update
• macOS: DMG (x64, arm64, universal), code signed + notarized
• Linux: AppImage (x64, arm64), .deb, .rpm, Snap
• GitHub Actions workflow - build on push/PR, release on tag
• Release artifacts uploaded to GitHub Releases
• Version derived from git tag (same scheme as Go goreleaser)
• Build matrix: 3 OS x 2 architectures = 6 targets
• Artifact size budget: under 100MB per installer
• Smoke test after build (launch and exit cleanly)