macOS build support

[Flo0806]

Description

Add macOS build support for DM Hero desktop app.

Requirements

• Build .dmg installer for macOS
• Support both Intel (x64) and Apple Silicon (arm64) architectures
• Code signing (optional but recommended for Gatekeeper)
• Update electron-builder config for macOS target
• Add macOS to GitHub Actions release workflow

Technical Notes

• electron-builder supports mac target with dmg and zip formats
• Universal binary possible with arch: ["x64", "arm64"] or "universal"
• Code signing requires Apple Developer account ($99/year) - can be skipped initially
• GitHub Actions has macos-latest runner available

Tasks

• Add macOS config to packages/app/package.json build section
• Update .github/workflows/release-app.yml for macOS builds
• Test native module (better-sqlite3) compilation on macOS
• Update landing page download section when ready

References

• electron-builder macOS docs
• better-sqlite3 build requirements