fix(mir): PHI検証panic修正 - update_cfg()を検証前に呼び出し

A案実装: debug_verify_phi_inputs呼び出し前にCFG predecessorを更新

修正箇所（7箇所）:
- src/mir/builder/phi.rs:50, 73, 132, 143
- src/mir/builder/ops.rs:273, 328, 351

根本原因:
- Branch/Jump命令でsuccessorは即座に更新
- predecessorはupdate_cfg()で遅延再構築
- PHI検証が先に実行されてpredecessor未更新でpanic

解決策:
- 各debug_verify_phi_inputs呼び出し前に
  if let Some(func) = self.current_function.as_mut() {
      func.update_cfg();
  }
  を挿入してCFGを同期

影響: if/else文、論理演算子(&&/||)のPHI生成が正常動作

lang/src/vm/boxes/flow_debugger.hako

@@ -11,7 +11,7 @@ using "lang/src/shared/common/string_helpers.hako" as StringHelpers
 
 static box FlowDebugBox {
   // ユーティリティ — 文字列検索
-  _index_of_from(hay, needle, pos) { if pos < 0 { pos = 0 } local n = hay.size() if pos > n { return -1 } local i = pos local m = needle.size() if m <= 0 { return pos } local limit = n - m loop(i <= limit) { if hay.substring(i, i+m) == needle { return i } i = i + 1 } return -1 }
+  _index_of_from(hay, needle, pos) { if pos < 0 { pos = 0 } local n = hay.length() if pos > n { return -1 } local i = pos local m = needle.length() if m <= 0 { return pos } local limit = n - m loop(i <= limit) { if hay.substring(i, i+m) == needle { return i } i = i + 1 } return -1 }
   _read_digits(text, pos) { return StringHelpers.read_digits(text, pos) }
   _int_to_str(n) { return StringHelpers.int_to_str(n) }
 
@@ -34,7 +34,7 @@ static box FlowDebugBox {
     if limit == null { limit = 50 }
     local ops = new ArrayBox()
     local pos = 0
-    loop(ops.size() < limit) {
+    loop(ops.length() < limit) {
       local p = me._index_of_from(mjson, "\"op\":\"", pos)
       if p < 0 { break }
       local q = me._index_of_from(mjson, "\"", p + 6)
@@ -50,9 +50,9 @@ static box FlowDebugBox {
   validate_cf_targets(mjson) {
     local ids = me.collect_block_ids(mjson)
     // Set 風マップ化
-    local idset = map({})
+    local idset = {}
     local i = 0
-    loop(i < ids.size()) { idset.set(ids.get(i), 1) i = i + 1 }
+    loop(i < ids.length()) { idset.set(ids.get(i), 1) i = i + 1 }
 
     local errs = new ArrayBox()
     local pos = 0
@@ -78,20 +78,20 @@ static box FlowDebugBox {
     }
 
     // レポート
-    if errs.size() == 0 { print("{\"kind\":\"flow_debug\",\"ok\":true,\"blocks\":" + (""+ids.size()) + "}") }
+    if errs.length() == 0 { print("{\"kind\":\"flow_debug\",\"ok\":true,\"blocks\":" + (""+ids.length()) + "}") }
     else {
       local k = 0
-      loop(k < errs.size()) { print("{\"kind\":\"flow_debug\",\"ok\":false,\"msg\":\"" + errs.get(k) + "\"}") k = k + 1 }
+      loop(k < errs.length()) { print("{\"kind\":\"flow_debug\",\"ok\":false,\"msg\":\"" + errs.get(k) + "\"}") k = k + 1 }
     }
-    return errs.size()
+    return errs.length()
   }
 
   // 要約: 先頭の op を列挙
   summarize_ops(mjson, limit) {
     local ops = me.collect_ops(mjson, limit)
     local i = 0
-    loop(i < ops.size()) { print("{\"kind\":\"flow_ops\",\"op\":\"" + ops.get(i) + "\"}") i = i + 1 }
-    return ops.size()
+    loop(i < ops.length()) { print("{\"kind\":\"flow_ops\",\"op\":\"" + ops.get(i) + "\"}") i = i + 1 }
+    return ops.length()
   }
 
   main(args) { return 0 }