R13: final sweep — EXEC stripping + INSPECT bugfix + more EQ assertions

1. Lark: preprocess strips EXEC CICS/SQL...END-EXEC blocks
   -> CI01_CICS/DB01_SELECT_UPDATE now parse, 75/75 samples pass
2. propagate_assignments INSPECT TALLYING bugfix:
   was reading source from count_var (wrong field) instead of
   asgn['tgt']. Now CNT='005' instead of '003' for len(HELLO)=5.
3. 26 new EQ/falsifiable assertions added (propagate chains,
   orchestrator state, data_writer, report generator)
4. Hardened: ACCEPT DATE string len check, DataWriter JSON format

16 suites / 0 FAIL.

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

cobol_testgen/read.py

@@ -31,6 +31,13 @@ def preprocess(source: str) -> str:
     # Lark 语法不支持 COPY（这是预处理指令），必须在解析前处理
     source = resolve_copybooks(source, '.')
 
+    # Strip EXEC ... END-EXEC blocks (CICS/SQL) before Lark parsing
+    source = re.sub(
+        r'EXEC\s+(?:CICS|SQL)\b.*?END-EXEC\.?',
+        '',
+        source, flags=re.IGNORECASE | re.DOTALL
+    )
+
     fixed = _is_fixed_format(source)
     lines = []
     for raw_line in source.splitlines():