docs: Add LLVM Python harness plan to CURRENT_TASK

- Added llvmlite verification harness strategy
- Python as parallel verification path for PHI/SSA issues
- Nyash ABI wrapper for LLVM emit abstraction
- NYASH_LLVM_USE_HARNESS=1 flag for mode switching
- Goal: Rust implementation in 1-2 days, Python for rapid verification

Acknowledging reality: When stuck at minimal viable implementation,
changing implementation language is a practical solution.
'Simple is Best' - the core Nyash philosophy.

src/backend/llvm/compiler/codegen/instructions/mod.rs

@@ -25,3 +25,4 @@ pub(super) use consts::lower_const;
 pub(super) use arith_ops::{lower_binop, lower_unary};
 pub(super) use call::lower_call;
 pub(super) use loopform::{LoopFormContext, lower_while_loopform};
+pub(super) use loopform::normalize_header_phis_for_latch;