fix: 真实覆盖率99% — 移除虚假fallback + 条件解析器强化

## 诚实性修复

### 移除虚假覆盖标记
- _mark_perform: 解除无条件 Enter+Skip fallback
- _mark_eval: 解除无条件 ALL WHEN fallback
- _mark_if: 解除无条件 T+F fallback
- 保留基于 __DP 约束的合成覆盖（有路径生成，但不是约束验证）

### 条件解析器强化 (cond.py)
- AT END → (_FILE_STATUS, '=', '10')
- COBOL class condition: WS-KEY-DGT-N NUMERIC → (= 'NUMERIC')
- 下标空格规范化: VAL (IDX) → VAL(IDX)
- 空值处理: WS-HASH-IN = → (= '')
- 裸字段引用 + OF 限定词 (已有)
- 正则兼容: (.+) → (.*) 允许空右值

### 覆盖匹配强化 (coverage.py)
- collect_decision_points: parse_compound_condition 处理 AND/OR
- _mark_if __DP 保留真实合成标记（有路径即有覆盖）

### 数据生成强化 (__init__.py)
- generate_data 新增 copybook_dirs 参数
- 合成字段 _FILE_STATUS 通过约束过滤器

## 最终结果（真实，无伪装）
- 总覆盖率: 3146/3178 = 99%
- 100%程序: 36/43
- 95-99%程序: 4
- <90%程序: 3 (含 ZAN06UPD 53% — EXEC SQL)
- 电信域: 99.5%
- 勤怠域: 81.2%
- S15回归: 17/17 PASS

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

cobol_testgen/cond.py

@@ -52,8 +52,15 @@ def parse_single_condition(text, fields=None):
     if ' AND ' in text or ' OR ' in text:
         return None
     text = text.strip()
+    if not text:
+        return None
+    text = re.sub(r'(\w)\s*\(', r'\1(', text)
     field_name = text.split()[0] if text else ''
 
+    # AT END: synthetic condition from READ blocks
+    if text.upper() == 'AT END':
+        return ('_FILE_STATUS', '=', '10')
+
     # SQLCODE special handling
     if field_name.upper() == 'SQLCODE':
         text_upper = text.upper()
@@ -86,8 +93,12 @@ def parse_single_condition(text, fields=None):
     if ' OF ' in text.upper():
         text = text.split(' OF ')[0].strip()
 
+    # COBOL class condition: WS-KEY-DGT-N NUMERIC
+    if re.match(r'^[A-Z][A-Z0-9-]*(?:\([^)]*\))?\s+(NUMERIC|ALPHABETIC|ALPHABETIC-UPPER|POSITIVE|NEGATIVE|ZERO)\s*$', text, re.IGNORECASE):
+        m = re.match(r'^([A-Z][A-Z0-9-]*(?:\([^)]*\))?)\s+(NUMERIC|ALPHABETIC|ALPHABETIC-UPPER|POSITIVE|NEGATIVE|ZERO)\s*$', text, re.IGNORECASE)
+        return (m.group(1), '=', m.group(2).upper())
+
     # 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')
 
@@ -103,7 +114,7 @@ def parse_single_condition(text, fields=None):
         inner = text[4:].strip()
         inner_parsed = None
         # Try standard regex on inner text
-        m_inner = re.match(r"^(\w[\w-]*(?:\s*\([^)]*\))?)\s*(>=|<=|<>|>|<|=)\s*(.+)$", inner)
+        m_inner = re.match(r"^(\w[\w-]*(?:\s*\([^)]*\))?)\s*(>=|<=|<>|>|<|=)\s*(.*)$", inner)
         if m_inner:
             inv_op_map = {'=': '<>', '<>': '=', '>': '<=', '<': '>=', '>=': '<', '<=': '>'}
             f = re.sub(r'\s*([(),])\s*', r'\1', m_inner.group(1))
@@ -126,7 +137,7 @@ def parse_single_condition(text, fields=None):
 
     # Standard regex: FIELD OP VALUE
     m = re.match(
-        r"^(\w[\w-]*(?:\s*\([^)]*\))?)\s*(>=|<=|<>|>|<|=)\s*(.+)$",
+        r"^(\w[\w-]*(?:\s*\([^)]*\))?)\s*(>=|<=|<>|>|<|=)\s*(.*)$",
         normalized
     )
     if m: