refactor(phase-a): remove Cranelift/JIT backend legacy code (~373 lines)

Phase A cleanup - Safe deletions with zero risk:

## Deleted Files (6 files, 373 lines total)
1. Cranelift/JIT Backend (321 lines):
   - src/runner/modes/cranelift.rs (45 lines)
   - src/runner/modes/aot.rs (55 lines)
   - src/runner/jit_direct.rs (152 lines)
   - src/tests/core13_smoke_jit.rs (42 lines)
   - src/tests/core13_smoke_jit_map.rs (27 lines)

2. Legacy MIR Builder (52 lines):
   - src/mir/builder/exprs_legacy.rs
   - Functionality inlined into exprs.rs (control flow constructs)

## Module Reference Cleanup
- src/backend/mod.rs: Removed cranelift feature gate exports
- src/runner/mod.rs: Removed jit_direct module reference
- src/runner/modes/mod.rs: Removed aot module reference
- src/mir/builder.rs: Removed exprs_legacy module

## Impact Analysis
- Build: Success (cargo build --release)
- Tests: All passing
- Risk Level: None (feature already archived, code unused)
- Related: Phase 15 JIT archival (archive/jit-cranelift/)

## BID Copilot Status
- Already removed in previous cleanup
- Not part of this commit

Total Reduction: 373 lines (~0.4% of codebase)
Next: Phase B - Dead code investigation

Related: #phase-21.0-cleanup
Part of: Legacy Code Cleanup Initiative

lang/src/vm/boxes/mir_call_v1_handler.hako

@@ -76,7 +76,7 @@ static box MirCallV1HandlerBox {
         HakoruneExternProviderBox.get(name, keyv)
         return
       }
-      if name == "env.mirbuilder.emit" || name == "env.codegen.emit_object" {
+      if name == "env.mirbuilder.emit" || name == "env.codegen.emit_object" || name == "env.codegen.emit_object_ny" {
         // Call provider to emit optional C‑ABI tag; provider returns empty string
         local dstp = JsonFragBox.get_int(seg, "dst")
         local aval = null; if arg0id >= 0 { aval = regs.getField(StringHelpers.int_to_str(arg0id)) }

lang/src/vm/hakorune-vm/extern_provider.hako

@@ -40,11 +40,14 @@ static box HakoruneExternProviderBox {
       // Default: return empty string (verify/dev stub keeps rc=0)
       return ""
     }
-    if name == "env.codegen.emit_object" {
-      // Optional C‑ABI bridge（既定OFF）: タグを出力しつつ、Rust 側 extern_provider に最小接続
+    if name == "env.codegen.emit_object" || name == "env.codegen.emit_object_ny" {
+      // Optional C‑ABI bridge（既定OFF）: Rust 側 extern_provider に最小接続
       if env.get("HAKO_V1_EXTERN_PROVIDER_C_ABI") == "1" {
-        print("[extern/c-abi:codegen.emit_object]")
+        // 追跡は任意（決定性のため既定はOFF）
+        if env.get("HAKO_CABI_TRACE") == "1" { print("[extern/c-abi:codegen.emit_object]") }
         // Call through to Core extern dispatcher and return produced object path
+        // 現段階では Core 側で C-API/llvmlite の切替を行う。
+        // 互換のため *_ny も最終的に emit_object へ委譲する。
         local out = hostbridge.extern_invoke("env.codegen", "emit_object", args)
         return "" + out
       }