feat: add COBOL statement benchmark plan and 34 P0 sample programs

- docs/cobol-statement-benchmark-plan.md — full coverage matrix and gap analysis
- 34 P0 COBOL samples: arithmetic(9), move(5), file(6), control(6),
  inspect(3), search(2), perform(3)
- test-data/validate_statements.py — automatic validation script
- Validation: 34/34 samples pass preprocess + extract_structure

test-data/cobol/statement_move/ST-MOVE-GROUP.cbl

@@ -0,0 +1,22 @@
+      * ==== TYPE: ST-MOVE-GROUP ====
+      * FEATURE: MOVE group-level (data propagation)
+      * STATEMENT: MOVE (group)
+      * BRANCHES: 2, DECISIONS: 1
+       IDENTIFICATION DIVISION.
+       PROGRAM-ID. MOVGRP.
+       DATA DIVISION.
+       WORKING-STORAGE SECTION.
+       01 WS-SOURCE.
+          05 WS-SRC-ID    PIC X(5) VALUE 'ITEM1'.
+          05 WS-SRC-AMT   PIC 9(5) VALUE 9999.
+       01 WS-DEST.
+          05 WS-DST-ID    PIC X(5).
+          05 WS-DST-AMT   PIC 9(5).
+       PROCEDURE DIVISION.
+       MAIN.
+           MOVE WS-SOURCE TO WS-DEST.
+           IF WS-DST-ID = 'ITEM1'
+               DISPLAY 'OK: GROUP MOVE ID'
+           ELSE
+               DISPLAY 'ERROR: GROUP MOVE'.
+           STOP RUN.