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/grammar.lark

@@ -7,14 +7,15 @@ FD_SUFFIX: /(?:"[^"]*"|'[^']*'|[^.])*\./
 working_storage: "WORKING-STORAGE" "SECTION" DOT data_item*
 linkage: "LINKAGE" "SECTION" DOT data_item*
 data_item: level_num (NAME | "FILLER") clause* DOT
-level_num: LEVEL
+level_num: INT
 clause: pic_clause | value_clause | occurs_clause | redefines_clause | usage_clause
       | "SYNC" | "SYNCHRONIZED"
       | "JUSTIFIED" "RIGHT"?
       | "BLANK" "WHEN" "ZERO"
       | "GLOBAL" | "EXTERNAL"
 pic_clause: "PIC" "IS"? PICTURE_STRING
-value_clause: "VALUE" "IS"? value_literal+
+value_clause: "VALUE" "IS"? value_list
+value_list: value_literal (","? value_literal)*
 value_literal: INT | SIGNED_NUMBER | STRING | SQSTRING
              | "ZERO" | "ZEROS" | "ZEROES"
              | "SPACE" | "SPACES"
@@ -27,9 +28,9 @@ key_clause: ("ASCENDING" | "DESCENDING") "KEY" "IS"? NAME (","? NAME)*
 indexed_clause: "INDEXED" "BY" NAME (","? NAME)*
 usage_clause: USAGE_VAL
 USAGE_VAL: "COMP" | "COMP-3" | "COMP-5" | "BINARY" | "PACKED-DECIMAL" | "DISPLAY"
-LEVEL: /0[1-9]|[1-4][0-9]|49|77|88/
+LEVEL: /0[1-9]|[0-4][0-9]|49|77|88|[0-9]+/
 NAME: /[A-Z][A-Z0-9-]*/i
-PICTURE_STRING: /[0-9A-Z()+,\-*\/V]+/i
+PICTURE_STRING: /[0-9A-Z()+,\-*\/V]+(?:\.[0-9A-Z()+,\-*\/V]+)?/i
 INT: /[0-9]+/
 DOT: /\./
 %import common.SIGNED_NUMBER