fix: jcl parse_jcl FileNotFoundError + module tests

BUG: parse_jcl() 文档说文件不存在时返回 None，
     但实际抛出了 FileNotFoundError。修复。

新增: test-data/step3_module_test.py — 未测试模块的首次实测
- comparator: API确认 (numeric/date/string 正确)
- jcl: 导入+tparse（发现FileNotFoundError bug）
- parametrized: matching(1:1/1:N/N:1) 数据生成
- storage: DiskCache/ReportStore set/get
- quality: L1OffsetValidator/L2RoundtripValidator
- agents: LLMClient 创建确认

验证: 66个COBOL样本全过管道(0崩溃/0无数据)

jcl/parser.py

@@ -44,8 +44,11 @@ COND_OPS = {
 
 def parse_jcl(filepath: str) -> Optional[Job]:
     """Parse a JCL file into a Job object."""
-    with open(filepath, "r", encoding="utf-8") as f:
-        lines = _merge_continuations(f.readlines())
+    try:
+        with open(filepath, "r", encoding="utf-8") as f:
+            lines = _merge_continuations(f.readlines())
+    except FileNotFoundError:
+        return None
 
     job = None
     current_step: Optional[JobStep] = None