✨ Python LLVM backend implementation (experimental)

- Created llvmlite-based LLVM backend in src/llvm_py/
- Implemented all MIR14 instructions (const, binop, jump, branch, ret, compare, phi, call, boxcall, externcall, typeop, newbox, safepoint, barrier)
- Experimental LoopForm support
- ~2000 lines of clean Python code vs complex Rust/inkwell
- Useful for PHI/SSA validation and rapid prototyping
- Added documentation to CLAUDE.md

This was created while waiting for ChatGPT's investigation of BuilderCursor issues.

src/llvm_py/instructions/const.py

@@ -42,7 +42,10 @@ def lower_const(
         # String constant - create global and get pointer
         i8 = ir.IntType(8)
         str_val = str(const_val)
-        str_const = ir.Constant.literal_string(str_val.encode('utf-8') + b'\0')
+        # Create array constant for the string
+        str_bytes = str_val.encode('utf-8') + b'\0'
+        str_const = ir.Constant(ir.ArrayType(i8, len(str_bytes)),
+                               bytearray(str_bytes))
         
         # Create global string constant
         global_name = f".str.{dst}"