Resolve all TODOs and stubs in codebase

[hyperpolymath]

• anv-ir/lower.rs: Detect flying and change_foot spin features from SpinFeature flags and SpinPositionDef properties
• anv-cli/main.rs: Implement full JSON serialization for parse command with program structure, segments, sequences, and elements
• anv-types/check.rs: Add pattern type checking for match expressions, implement step sequence validation, lift group level validation, throw rotation/type validation, and refinement type predicate checking