fix: 覆盖率统计全面修复 + 5漏洞修正

## 修复内容

### C1: _mark_eval 反向操作符 (coverage.py)
- EVALUATE 约束匹配支持  操作符
- WHEN OTHER 的自动检测（全部 WHEN 被否定时）

### C2: _mark_perform 反向操作符 (coverage.py)
- PERFORM 同 _mark_if 的反向操作符匹配
- PERFORM UNTIL 条件截断后桥接器通过 branch_names 识别类型

### H1: parse_single_condition 传递 fields (coverage.py)
- collect_decision_points 调用时传 fields 参数
- NOT 前缀条件解析 (NOT WS-X > 50 → WS-X <= 50)

### H4: generate_data 输入约束 (__init__.py)
- 文档注明接收原始源码，非预处理后文本

### M1: not_map break (cond.py)
- NOT 操作符映射循环添加 break

## 覆盖测试结果
- IF: 100% (T/F)
- NOT IF: 100% (NOT_TRUE/NOT_FALSE)
- PERFORM UNTIL: 100% (ENTER/SKIP)
- EVALUATE: 100% (4 WHENs)
- Nested IF: 100% (4 branches)
- S15 回归: 17/17 PASS

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

cobol_testgen/pipeline_bridge.py

@@ -99,13 +99,15 @@ def _convert_node(node: BranchNode, parent: BrSeq):
 
     if k == "PERFORM":
         cond = node.condition_text or ""
-        u = cond.upper()
-        if 'VARYING' in u:
+        br_names = [b.upper() for b in node.branch_names] if node.branch_names else []
+        if any('VARY' in b for b in br_names):
             br = BrPerform("varying", condition=cond)
-        elif 'UNTIL' in u:
+        elif any('SKIP' in b or 'ENTER' in b for b in br_names):
             br = BrPerform("until", condition=cond)
-        else:
+        elif any('TIMES' in b for b in br_names):
             br = BrPerform("times", condition=cond)
+        else:
+            br = BrPerform("until", condition=cond)
         for c in node.children: _convert_node(c, br.body_seq)
         parent.add(br)
         return