Summary

• Zero-capture tagged variants now use Void type instead of empty struct
• JSON output omits $data field for void variants: {"$tag":"Empty"}
• TypeScript types omit $data field: interface QEmpty { $tag: "Empty" }

Before/After

// Before
{"$tag":"Empty","$data":{}}
interface QEmpty { $tag: "Empty"; $data: {} }

// After  
{"$tag":"Empty"}
interface QEmpty { $tag: "Empty" }

Changes

• infer.rs: Use TYPE_VOID for zero-capture variants
• value.rs: Make Tagged.data optional, skip serialization when None
• materializer.rs: Track payload type, produce None for Void
• typescript.rs: Omit $data field for Void variants
• type-system.md: Updated documentation