Phase 11-12: LLVM backend initial, semantics layer, plugin unification

Major changes:
- LLVM backend initial implementation (compiler.rs, llvm mode)
- Semantics layer integration in interpreter (operators.rs)
- Phase 12 plugin architecture revision (3-layer system)
- Builtin box removal preparation
- MIR instruction set documentation (26→Core-15 migration)
- Cross-backend testing infrastructure
- Await/nowait syntax support

New features:
- LLVM AOT compilation support (--backend llvm)
- Semantics layer for interpreter→VM flow
- Tri-backend smoke tests
- Plugin-only registry mode

Bug fixes:
- Interpreter plugin box arithmetic operations
- Branch test returns incorrect values

Documentation:
- Phase 12 README.md updated with new plugin architecture
- Removed obsolete NYIR proposals
- Added LLVM test programs documentation

Co-Authored-By: Claude <noreply@anthropic.com>

build_llvm_wsl_msvc.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+# Build Windows exe with LLVM from WSL using cross compilation
+
+echo "Setting up Windows cross-compilation with LLVM..."
+
+# Set environment variables for WSL cross-compilation
+export LLVM_SYS_180_PREFIX="C:\\LLVM-18"
+export LLVM_SYS_180_FFI_WORKAROUND="1"
+export LLVM_SYS_NO_LIBFFI="1"  # This is the key!
+
+# Use cargo-xwin for cross compilation
+echo "Building nyash.exe for Windows with LLVM support..."
+cargo xwin build --target x86_64-pc-windows-msvc --release --features llvm -j32
+
+# Check if successful
+if [ -f "target/x86_64-pc-windows-msvc/release/nyash.exe" ]; then
+    echo "Build successful!"
+    ls -la target/x86_64-pc-windows-msvc/release/nyash.exe
+else
+    echo "Build failed - nyash.exe not found"
+    echo "Checking what was built:"
+    ls -la target/x86_64-pc-windows-msvc/release/ 2>/dev/null || echo "Target directory not found"
+fi