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

docs/ENV_VARS.md

@@ -2,6 +2,10 @@
 
 This document lists the environment flags introduced or used by the Phase 22.1 work. Defaults are OFF and behavior remains unchanged unless noted.
 
+- NYASH_JSON_ONLY=0|1
+  - Quiet JSON pipelines: suppresses `RC:` and routine logs on stdout (diagnostics still go to stderr).
+  - Used by Stage‑B → Program(JSON) emit to keep the output clean for downstream processing.
+
 - HAKO_USING_SSOT=0|1
   - Enables the SSOT resolver gate in the runner pipeline.
   - When ON, resolution first consults the SSOT bridge (modules-only MVP). If not resolved, it falls back to the existing resolver.
@@ -91,13 +95,34 @@ LLVM backend selector (builder wrapper)
   - `crate`: uses `./target/release/ny-llvmc` (build with `cargo build -p nyash-llvm-compiler --release`).
   - `native`: reserved for future Hako-native builder.
   - Linking extras for `--emit exe`: pass via `HAKO_AOT_LDFLAGS` (e.g., `-static`), `ny-llvmc` consumes `--libs`.
+  - Note: crate 経路では ny_main の戻り値（i64）がプロセスの終了コードに反映されます（rc mapping）。
+
+- HAKO_LLVM_CANARY_NORMALIZE=0|1
+  - 開発/カナリア専用の正規化スイッチ。`1` のとき、最小の JSON 形状差（`schema_version=1` → `"1.0"`、`blocks.inst` → `instructions`、`const` の `ty/value` 包装）を自動補正してからビルドします。
+  - 既定は `0`（無効）。既存ツールの挙動は変わりません。`NYASH_CLI_VERBOSE=1` のとき形状ヒントを `[ny-llvmc/hint]` で出力します。
 
 Name mapping note (EXE link convenience)
 - nyash.console.* は C リンク時にシンボル名 `nyash_console_*` に正規化される（ドット→アンダースコア）。
   - 例: `externcall nyash.console.log(i8*)` → C シンボル `nyash_console_log`。
   - 最小 C ランタイム（Phase 22.3）の `nyash-kernel-min-c` は `nyash_console_log(char*)` を提供（設計段階）。
-
+  
 Kernel Minimal C Runtime (Phase 22.3 — design)
 - NYASH_KERNEL_C_MIN=0|1
   - Reserved toggle for enabling the minimal C runtime shims（design‑stage; defaults OFF）
   - Build: `cargo build --release -p nyash-kernel-min-c`（not linked by default）
+
+ENV consolidation (aliases)
+- NY compiler path
+  - Primary: `NYASH_USE_NY_COMPILER=0|1`
+  - Accepted aliases (deprecated; prints a one‑time warning):
+    - `NYASH_DISABLE_NY_COMPILER=1` → equivalent to `NYASH_USE_NY_COMPILER=0`
+    - `HAKO_DISABLE_NY_COMPILER=1` → equivalent to `NYASH_USE_NY_COMPILER=0`
+- LLVM opt level
+  - Primary: `NYASH_LLVM_OPT_LEVEL`
+  - Accepted alias (deprecated; one‑time warning): `HAKO_LLVM_OPT_LEVEL`
+- Gate‑C (Core direct route)
+  - Primary: `NYASH_GATE_C_CORE`
+  - Accepted alias (deprecated; one‑time warning): `HAKO_GATE_C_CORE`
+
+Notes
+- Primary keys are preferred and will be kept. Aliases remain accepted for a grace period and emit a concise deprecation line once per process.