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-INI-MULTI.cbl

@@ -0,0 +1,19 @@
+      * ==== TYPE: ST-INI-MULTI ====
+      * FEATURE: INITIALIZE multiple fields
+      * STATEMENT: INITIALIZE
+      * BRANCHES: 2, DECISIONS: 1
+       IDENTIFICATION DIVISION.
+       PROGRAM-ID. INIMUL.
+       DATA DIVISION.
+       WORKING-STORAGE SECTION.
+       01 WS-NAME    PIC X(10) VALUE 'HELLO'.
+       01 WS-COUNT   PIC 9(5) VALUE 12345.
+       01 WS-FLAG    PIC X    VALUE 'Y'.
+       PROCEDURE DIVISION.
+       MAIN.
+           INITIALIZE WS-NAME WS-COUNT WS-FLAG.
+           IF WS-NAME = SPACES
+               DISPLAY 'OK: INITIALIZE NAME'
+           ELSE
+               DISPLAY 'ERROR: INITIALIZE'.
+           STOP RUN.