Add native macOS builds and packaging support

[shadowbipnode]

Add official macOS support with Electron packaging and platform compatibility validation.

Goals:

• dmg packaging
• Apple Silicon testing
• Intel compatibility validation
• safeStorage verification
• sandbox/security adjustments
• UI consistency checks

[shadowbipnode]

macOS packaging support remains planned, but is being deprioritized until there is stronger demand from real-world users.

Current focus:

• operational workflows
• Windows/Linux packaging
• UX stabilization
• local-first infrastructure tooling