S14: 58-program benchmark suite — Lark grammar fixes + external COBOL validation

Grammar fixes:
1. COPY regex: handle quoted names COPY "STD-REC.CPY"
2. Quoted name strip: remove quotes before file lookup
3. VALUE clause: support comma-separated 88-level values
4. PIC STRING: support decimal dot (ZZ9.99 -> PICTURE_STRING.99 + DOT)
5. LEVEL: use INT for level number (fixes 05/01/77 all levels)

Results on 58 telecom billing COBOL programs:
- Parse OK: 54/58 (93%)
- Parse fail: 4 (special chars: TAB, X'01', U'NNNN', &)
- Classification known issue: matching programs misclassified as
  '文件编成' because FILE-CONTROL keyword overrides matching signals
  (requires rule engine priority fix - separate issue)

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

cobol_testgen/read.py

@@ -95,7 +95,7 @@ _COPYBOOK_EXTENSIONS = ['.cpy', '.cbl', '.cpb', '']
 def resolve_copybooks(source: str, source_dir: str, _recursion_depth: int = 0) -> str:
     """Find COPY statements and replace with copybook content."""
     _RE_COPY = re.compile(
-        r"^\s*COPY\s+(\w[\w-]*)(?:\s+REPLACING\s+(.+?))?\s*\.?\s*$",
+        r"^\s*COPY\s+(\w[\w-]*|\"[^\"]*\"|\'[^\']*\')(?:\s+REPLACING\s+(.+?))?\s*\.?\s*$",
         re.IGNORECASE
     )
     _RE_PAIR = re.compile(r"==(.+?)==\s+BY\s+==(.+?)==", re.IGNORECASE)
@@ -105,7 +105,8 @@ def resolve_copybooks(source: str, source_dir: str, _recursion_depth: int = 0) -
     for line in lines:
         m = _RE_COPY.match(line)
         if m:
-            name = m.group(1).upper()
+            raw_name = m.group(1)
+            name = raw_name.strip('"').strip("'").upper()
             found = None
             for ext in _COPYBOOK_EXTENSIONS:
                 p = Path(source_dir, name + ext)