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

CHANGELOG.md

@@ -36,3 +36,9 @@ Notes
   - Python LLVM builder fixes: cmp field normalization (Lt/Le/… → < <= …), ret PHI synthesis (avoid ret=0), flat mir_call shape acceptance.
 - Using/alias polish (prod): modules mapping preferred; missing module aliases added (StrCast / MethodAliasPolicy). Duplicate using in VM extern_provider cleaned.
 - Docs: phase‑21.0 marked COMPLETE (Quick Verify updated). CURRENT_TASK closed.
+
+## 2025‑11‑06 — Phase 21.1 (LLVM C‑API emit‑only) finalize
+- C‑API path green for both reps (ternary rc=44 / map set→size rc=1). `tools/smokes/v2/profiles/quick/core/phase2111/run_all.sh` runs both.
+- VM handler cleanup (SSOT): removed duplicated `hostbridge.extern_invoke` branches in `calls.rs`; all externs route through `extern_provider_dispatch`.
+- Trace polish: consolidated `[hb:*]` to low‑noise, gated by `HAKO_CABI_TRACE=1`.
+- Docs updated: phase‑21.1 README set to COMPLETE with Quick Verify and troubleshooting.