feat(control_tree): Phase 131 P1.5-P2 DirectValue exit reconnection

Implement DirectValue mode for Normalized shadow exit handling:

**P1.5 Changes**:
- Add ExitReconnectMode::DirectValue (skip exit PHI generation)
- Carry remapped_exit_values through merge result
- Update host variable_map directly with exit values
- Fix loop(true) { x = 1; break }; return x to return 1 correctly

**P2 Changes**:
- Normalize k_exit continuation entry/exit edges
- Rewrite TailCall(k_exit) → Jump(exit_block) for proper merge
- Add verify_all_terminator_targets_exist contract check
- Extend ExitLineReconnector to handle DirectValue mode

**Infrastructure**:
- tools/build_llvm.sh: Force TMPDIR under target/ (EXDEV mitigation)
- llvm_exe_runner.sh: Add exit_code verification support
- Phase 131 smokes: Update for dev-only + exit code validation

**Contracts**:
- PHI-free: Normalized path uses continuations only
- Exit values reconnect via remapped ValueIds
- Existing patterns unaffected (既定挙動不変)

Related: Phase 131 loop(true) break-once Normalized support

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/mir/builder/control_flow/joinir/patterns/exit_binding.rs

@@ -383,6 +383,7 @@ mod tests {
             expr_result: None,          // Phase 33-14: Add missing field
             loop_var_name: None,        // Phase 33-16: Add missing field
             carrier_info: None,         // Phase 228: Add missing field
+            exit_reconnect_mode: crate::mir::join_ir::lowering::carrier_info::ExitReconnectMode::default(), // Phase 131 P1.5
         };
 
         builder

src/mir/builder/control_flow/joinir/patterns/exit_binding_applicator.rs

@@ -137,6 +137,7 @@ mod tests {
             expr_result: None,          // Phase 33-14: Add missing field
             loop_var_name: None,        // Phase 33-16: Add missing field
             carrier_info: None,         // Phase 228: Add missing field
+            exit_reconnect_mode: crate::mir::join_ir::lowering::carrier_info::ExitReconnectMode::default(), // Phase 131 P1.5
         };
 
         apply_exit_bindings_to_boundary(&carrier_info, &exit_meta, &variable_map, &mut boundary)