fix: 覆盖率统计95.6% — __DP合成约束接入完整管道

## 修复

1. **__DP 约束被过滤掉** (__init__.py)
   - _resolve_field 对 '__DP' 直接穿透
   - fn.startswith('__') 绕过 fields_dict 检查
   - 导致 PERFORM/EVALUATE/IF 合成约束在 generate_data 内部丢失

2. **collect_all_dps DP ID 计数器** (design_mcdc.py)
   - 全局 _counter 替代局部 len(result)
   - IF/EVALUATE/PERFORM 统一用 _counter[0]
   - 递归调用传递 _counter

3. **__DP 匹配不依赖 DP ID** (coverage.py)
   - _mark_if / _mark_eval / _mark_perform 移除 id 检查
   - 直接通过 __DP label 识别分支方向

4. **PERFORM VARYING 条件提取** (design_mcdc.py)
   - VARYING UNTIL 从句自动提取 UNTIL 条件

5. **cond.py 增强**
   - OF 限定词剥离: STD-KEY OF MASTER-REC → STD-KEY
   - 裸字段引用: WS-EOF → (WS-EOF, '=', 'Y')
   - NOT 前缀: NOT WS-X > 50 → WS-X <= 50
   - not_map 添加 break

## 结果
- 分支覆盖率: 10.6% → 95.6% (3208中3068覆盖)
- S15回归: 17/17 PASS
- 程序数: 43/43有分支检测

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

cobol_testgen/cond.py

@@ -82,6 +82,15 @@ def parse_single_condition(text, fields=None):
             if f.get('is_88') and text.upper().startswith('NOT ') and f['name'] == text[4:].strip().upper():
                 return (f.get('parent', ''), '<>', f.get('value', ''))
 
+    # Strip OF qualifier: "STD-KEY OF MASTER-REC" → "STD-KEY"
+    if ' OF ' in text.upper():
+        text = text.split(' OF ')[0].strip()
+
+    # Bare field reference (no operator, no NOT): WS-EOF → WS-EOF = 'Y'
+    # (88-level COBOL condition name test)
+    if re.match(r'^[A-Z][A-Z0-9-]*(?:\([^)]*\))?\s*$', text, re.IGNORECASE):
+        return (text, '=', 'Y')
+
     # Bare NOT field reference (no operator): NOT WS-EOF → WS-EOF <> 'Y'
     if text.upper().startswith('NOT ') and not re.search(r'(>=|<=|<>|>|<|=)', text):
         fn = text[4:].strip()