feat: LLVM native compilation backend

[ardeshir]

Summary

• Adds llvm-backend/ — LLVM 18 native compilation for DOL programs
• New dol-native CLI tool with build, emit-ir, and targets subcommands
• HIR-to-LLVM-IR lowering engine (hir_lowering.rs) wired to the DOL parser
• 5 target architectures: ARM64 Linux, ARM64 macOS, RISC-V 64, x86-64 Linux, x86-64 Windows
• 22 VUDO ABI host function declarations (I/O, Memory, Time, Messaging, Random, Effects, Debug)
• 11 native examples demonstrating what compiles today
• User manual at docs/native-compilation.md

What compiles end-to-end

• Functions with parameters, return types, recursion
• Integer/boolean arithmetic (14 binary ops, 2 unary ops)
• if/else control flow
• Genes → LLVM struct types (typed fields + heuristic inference)
• Traits, rules, systems (compile-time validation, no runtime code)
• String literals and print/println via VUDO ABI
• Val bindings and local variables
• Cross-compilation to all 5 targets from a single source

What needs stdlib / library work

Gap	What's Needed
String concatenation (+)	dol_string_concat in stdlib
.to_string()	Type-specific formatters
Vec<T>, Map<K,V>	Collection implementations
for / while loops	Loop codegen in hir_lowering
match expressions	Branch/jump table codegen
mut variables	Parser support
Method dispatch	Vtable or monomorphized calls
Field/index access	Struct GEP codegen
CRDT implementations	Library crate for peritext, rga, etc.
Spirit manifests	Parser + package manager
+=, path syntax (::)	Parser extensions

Test results

• univrs-dol: 2,074 tests pass, 0 failures
• llvm-backend: 10 tests pass (abi, functions, structs, types, targets, hir_lowering, codegen)
• Native examples: 11/11 emit valid LLVM IR
• Existing .dol files: 93/155 compile through native pipeline (62 use features needing parser/stdlib work)

Test plan

• cargo test --all in univrs-dol (2,074 pass)
• cargo test --all in llvm-backend (10 pass)
• dol-native emit-ir on all 11 native examples
• dol-native build produces valid ELF x86-64 object files
• dol-native targets lists all 5 architectures
• CI: llvm-backend tests require LLVM 18 (separate CI job needed)