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

src/tokenizer/engine.rs

@@ -3,12 +3,15 @@ use super::{NyashTokenizer, Token, TokenType, TokenizeError};
 impl NyashTokenizer {
     #[inline]
     pub(crate) fn allow_semicolon() -> bool {
+        // Default: ON (semicolon is an optional statement separator)
+        // Allow opt-out via NYASH_PARSER_ALLOW_SEMICOLON=0|false|off
         match std::env::var("NYASH_PARSER_ALLOW_SEMICOLON").ok() {
             Some(v) => {
                 let lv = v.to_ascii_lowercase();
-                lv == "1" || lv == "true" || lv == "on"
+                if lv == "0" || lv == "false" || lv == "off" { return false; }
+                true
             }
-            None => false,
+            None => true,
         }
     }