Phase 22.x WIP: LLVM backend improvements + MIR builder enhancements

LLVM backend improvements:
- Add native LLVM backend support (NYASH_LLVM_BACKEND=native)
- Add crate backend selector with priority (crate > llvmlite)
- Add native_llvm_builder.py for native IR generation
- Add NYASH_LLVM_NATIVE_TRACE=1 for IR dump

MIR builder enhancements:
- Refactor lower_if_compare_* boxes for better code generation
- Refactor lower_return_* boxes for optimized returns
- Refactor lower_loop_* boxes for loop handling
- Refactor lower_method_* boxes for method calls
- Update pattern_util_box for better pattern matching

Smoke tests:
- Add phase2100 S3 backend selector tests (17 new tests)
- Add phase2120 native backend tests (4 new tests)
- Add phase2034 MIR builder internal tests (2 new tests)
- Add phase2211 TLV shim parity test

Documentation:
- Update ENV_VARS.md with LLVM backend variables
- Update CURRENT_TASK.md with progress
- Update README.md and CHANGELOG.md

Config:
- Add NYASH_LLVM_BACKEND env support in src/config/env.rs
- Update ny_mir_builder.sh for backend selection
- Update dispatch.rs for backend routing

Tools:
- Add tools/native_llvm_builder.py
- Update smokes/v2/profiles/quick/core/phase2100/run_all.sh

Known: Many Hako builder internal files modified for optimization

CHANGELOG.md

@@ -3,6 +3,14 @@
 This changelog tracks high‑level milestones while Core MIR and Phase 12 evolve. For detailed per‑file history, see git log and docs under `docs/development/roadmap/`.
 
 ## 2025‑09‑06
+
+### Phase 22.3 (Kernel Minimal C Runtime — design wrap)
+- Added minimal C runtime crate (design-stage): `crates/nyash_kernel_min_c` (staticlib).
+- LLVM extern lowering: normalized `nyash.console.*` → `nyash_console_*` for C linkage.
+- Hako-first MIR emit stabilized via wrapper (`tools/hakorune_emit_mir.sh`): Stage‑B JSON is emitted with `NYASH_JSON_ONLY=1` and sanitized; builder falls back to Rust CLI on failure (defaults keep quick green).
+
+### Prep for Phase 21.10 (LLVM line — crate backend)
+- Backend selector and S3 canaries exist; print EXE canary currently SKIP pending small normalization. Next: enable print EXE PASS with env‑guarded normalization in ny‑llvmc (no default behavior changes).
 - Core‑13 flip complete: code/tests enforce Core‑13 minimal kernel. Normalizations (Array/Ref→BoxCall, TypeCheck/Cast/Barrier/WeakRef unification) are ON by default via env (NYASH_MIR_CORE13=1). New tests validate normalization.
 - Docs synced: step‑50 marked done; DEV quickstart points to Core‑13 reference.