fix: 无连字符 KEY 变量 + COBOL 专家 10 大攻击面测试

COBOL 专家对抗性审查发现:
- 老式 COBOL 的 WSKEY1/WSKEY2（无连字符）未被 L1 关键词检测
- 结构性检测信号 4 和 5 覆盖不全

修复:
- L1 增加 re:WS[A-Z0-9]*KEY[A-Z0-9]* 覆盖无连字符 KEY 命名
- _matches_key_comparison 扩展支持无连字符变量
- has_key_var 注入扩展支持无连字符
- 结构性检测信号 4 增加 WS\w+ 比较模式
- 结构性检测信号 5 增加两个单独 OPEN 的支持

新测试:
- test_cobol_expert_attacks — 4 个内联攻击测试
  (跨行AT END, 无连字符WSKEY, GO TO风格, NOT=比较)
- test-adversarial: 8 个样本文件攻击测试

全回归: 767 passed (+3 new, 0 failures)

test-data/cobol/adversarial/ADV-OLD-SCHOOL.cbl

@@ -0,0 +1,35 @@
+      * ==== TYPE: ADV-MATCH-OLDSCHOOL ====
+      * FEATURE: Real matching program but uses different
+      *          naming convention (K01-, not WS-)
+      * STATEMENT: IF / READ / OPEN
+      * BRANCHES: 2, DECISIONS: 1
+      * ADVERSARIAL: KEY variables not prefixed WS-
+       IDENTIFICATION DIVISION.
+       PROGRAM-ID. KSMTCH.
+       ENVIRONMENT DIVISION.
+       INPUT-OUTPUT SECTION.
+       FILE-CONTROL.
+           SELECT FILE-A ASSIGN TO 'FILEA.DAT'.
+           SELECT FILE-B ASSIGN TO 'FILEB.DAT'.
+       DATA DIVISION.
+       FILE SECTION.
+       FD FILE-A.
+       01 REC-A PIC X(80).
+       FD FILE-B.
+       01 REC-B PIC X(80).
+       WORKING-STORAGE SECTION.
+       01 K01-KEY    PIC X(10).
+       01 K02-KEY    PIC X(10).
+       01 WS-EOF1    PIC X VALUE 'N'.
+       01 WS-EOF2    PIC X VALUE 'N'.
+       PROCEDURE DIVISION.
+       MAIN.
+           OPEN INPUT FILE-A FILE-B.
+           READ FILE-A INTO REC-A AT END MOVE 'Y' TO WS-EOF1.
+           READ FILE-B INTO REC-B AT END MOVE 'Y' TO WS-EOF2.
+           IF K01-KEY = K02-KEY
+               DISPLAY 'MATCH'
+           ELSE
+               DISPLAY 'NO MATCH'.
+           CLOSE FILE-A FILE-B.
+           STOP RUN.