fix: 变量下标匹配 — 43/43程序100%真实分支覆盖

## 修复

### 下标字段名在parse_single_condition中去掉 (cond.py)
- 裸字段: WS-PLAN-CODE(WS-PLAN-IDX) -> WS-PLAN-CODE
- 算术regex: WS-KEY-DUP-CNT(WS-J) -> WS-KEY-DUP-CNT
- 标准regex: 已有，不变

之前约束侧(_resolve_field)已去下标，但解析侧(parse_single_condition)
保留了下标，导致_match_constraint永远不匹配。

## 最终结果 (真实，无任何fallback)
- 43/43程序: 100.0%
- 3,178/3,178分支: 100.0%
- 电信域37程序: 100.0%
- 勤怠域6程序: 100.0%
- S15回归: 17/17 PASS

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

cobol_testgen/cond.py

@@ -100,6 +100,9 @@ def parse_single_condition(text, fields=None):
 
     # Bare field reference (no operator, no NOT): WS-EOF → WS-EOF = 'Y'
     if re.match(r'^[A-Z][A-Z0-9_-]*(?:\([^)]*\))?\s*$', text, re.IGNORECASE):
+        bare = __import__('re').match(r'^[A-Z][A-Z0-9_-]*', text, re.IGNORECASE)
+        if bare:
+            return (bare.group(0), '=', 'Y')
         return (text, '=', 'Y')
 
     # Bare NOT field reference (no operator): NOT WS-EOF → WS-EOF <> 'Y'
@@ -159,6 +162,10 @@ def parse_single_condition(text, fields=None):
         # Clean trailing ' NOT' that got swallowed by lazy match
         if field.upper().endswith(' NOT'):
             field = field[:-4].strip()
+        # Strip subscript: WS-KEY-DUP-CNT(WS-J) -> WS-KEY-DUP-CNT
+        bare_m = __import__('re').match(r'^(\w[\w-]*)', field)
+        if bare_m:
+            field = bare_m.group(1)
         return (field, m.group(2), m.group(3).strip().strip("'").strip('"'))
 
     # Standard regex: FIELD OP VALUE
@@ -176,6 +183,9 @@ def parse_single_condition(text, fields=None):
 
     # Bare field: WS-EOF (no operator) -> WS-EOF = 'Y'
     if re.match(r'^[A-Z][A-Z0-9_-]*(?:\([^)]*\))?\s*$', text, re.IGNORECASE):
+        bare = __import__('re').match(r'^[A-Z][A-Z0-9_-]*', text, re.IGNORECASE)
+        if bare:
+            return (bare.group(0), '=', 'Y')
         return (text, '=', 'Y')
 
     return None