Theme Studio: token engine and design system architecture

[SunilKumarKV]

Create RainbowCode token engine.

Includes:

• Colors
• Typography
• Spacing
• Radius
• Shadows
• Theme serialization
• Theme export format

Supports:

• Glass
• SaaS
• Gaming
• Luxury
• Minimal
• Neon

Acceptance:

• Token schema versioning
• JSON export
• Type-safe access