axon-frontend 0.4.0

AXON compiler frontend — lexer, parser, AST, epistemic type system, type checker, IR generator, compile-time checker. Zero runtime dependencies. v0.4.0 closes Fase 17.a/17.d (let runtime wiring): LetStatement.value_kind + IRLetBinding.value_kind preserve parser tokenization intent so the runtime dispatcher can distinguish a quoted literal from a dotted-identifier reference; type_checker adds reserved-primitive-name shadowing + self-reference rejection for let bindings (Rust mirror of Python). v0.3.0 closed Fase 14 (lossless lexing). v0.2.0 added Fase 13 typed channels.