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_control/ST-CALL-CONTENT.cbl

@@ -0,0 +1,17 @@
+      * ==== TYPE: ST-CALL-CONTENT ====
+      * FEATURE: CALL ... BY CONTENT
+      * STATEMENT: CALL BY CONTENT
+      * BRANCHES: 2, DECISIONS: 1
+       IDENTIFICATION DIVISION.
+       PROGRAM-ID. CALLCN.
+       DATA DIVISION.
+       WORKING-STORAGE SECTION.
+       01 WS-PARAM  PIC 9(5) VALUE 100.
+       PROCEDURE DIVISION.
+       MAIN.
+           CALL 'SUBPGM' USING BY CONTENT WS-PARAM.
+           IF WS-PARAM = 100
+               DISPLAY 'OK: BY CONTENT'
+           ELSE
+               DISPLAY 'ERROR: BY CONTENT'.
+           STOP RUN.

test-data/cobol/statement_control/ST-CALL-VALUE.cbl

@@ -0,0 +1,20 @@
+      * ==== TYPE: ST-CALL-VALUE ====
+      * FEATURE: CALL ... BY VALUE with mixed mechanisms
+      * STATEMENT: CALL BY VALUE
+      * BRANCHES: 2, DECISIONS: 1
+       IDENTIFICATION DIVISION.
+       PROGRAM-ID. CALLVL.
+       DATA DIVISION.
+       WORKING-STORAGE SECTION.
+       01 WS-A PIC 9(5) VALUE 10.
+       01 WS-B PIC 9(5) VALUE 20.
+       PROCEDURE DIVISION.
+       MAIN.
+           CALL 'SUBPGM' USING
+               BY VALUE WS-A
+               BY REFERENCE WS-B.
+           IF WS-A = 10
+               DISPLAY 'OK: BY VALUE'
+           ELSE
+               DISPLAY 'ERROR: BY VALUE'.
+           STOP RUN.

test-data/cobol/statement_control/ST-EVAL-ALSO.cbl

@@ -0,0 +1,22 @@
+      * ==== TYPE: ST-EVAL-ALSO ====
+      * FEATURE: EVALUATE ALSO (multiple subjects)
+      * STATEMENT: EVALUATE ALSO
+      * BRANCHES: 4, DECISIONS: 1
+       IDENTIFICATION DIVISION.
+       PROGRAM-ID. EVLALS.
+       DATA DIVISION.
+       WORKING-STORAGE SECTION.
+       01 WS-STATUS  PIC X(1) VALUE 'A'.
+       01 WS-TYPE    PIC X(1) VALUE 'X'.
+       PROCEDURE DIVISION.
+       MAIN.
+           EVALUATE WS-STATUS ALSO WS-TYPE
+               WHEN 'A' ALSO 'X'
+                   DISPLAY 'OK: A-X'
+               WHEN 'A' ALSO 'Y'
+                   DISPLAY 'A-Y'
+               WHEN 'B' ALSO ANY
+                   DISPLAY 'B-ANY'
+               WHEN OTHER
+                   DISPLAY 'OTHER'.
+           STOP RUN.

test-data/cobol/statement_control/ST-GOTO-DEPEND.cbl

@@ -0,0 +1,25 @@
+      * ==== TYPE: ST-GOTO-DEPENDING ====
+      * FEATURE: GO TO ... DEPENDING ON
+      * STATEMENT: GO TO DEPENDING ON
+      * BRANCHES: 0, DECISIONS: 1
+      * NOTE: GO TO DEPENDING ON is parsed as pass-through (no IF branches)
+       IDENTIFICATION DIVISION.
+       PROGRAM-ID. GTODEP.
+       DATA DIVISION.
+       WORKING-STORAGE SECTION.
+       01 WS-SEL    PIC 9(1) VALUE 2.
+       PROCEDURE DIVISION.
+       MAIN.
+           GO TO PARA-1 PARA-2 PARA-3
+               DEPENDING ON WS-SEL.
+           DISPLAY 'FALL THROUGH'.
+           STOP RUN.
+       PARA-1.
+           DISPLAY 'PARA-1'.
+           STOP RUN.
+       PARA-2.
+           DISPLAY 'PARA-2'.
+           STOP RUN.
+       PARA-3.
+           DISPLAY 'PARA-3'.
+           STOP RUN.

test-data/cobol/statement_control/ST-IF-COMP.cbl

@@ -0,0 +1,22 @@
+      * ==== TYPE: ST-IF-COMP ====
+      * FEATURE: IF with compound conditions (AND / OR)
+      * STATEMENT: IF (compound)
+      * BRANCHES: 4, DECISIONS: 2
+       IDENTIFICATION DIVISION.
+       PROGRAM-ID. IFCOMP.
+       DATA DIVISION.
+       WORKING-STORAGE SECTION.
+       01 WS-A       PIC 9(5) VALUE 100.
+       01 WS-B       PIC 9(5) VALUE 200.
+       01 WS-C       PIC 9(5) VALUE 10.
+       PROCEDURE DIVISION.
+       MAIN.
+           IF WS-A > 50 AND WS-B > 100
+               DISPLAY 'OK: AND CONDITION'
+           ELSE
+               DISPLAY 'ERROR: AND'.
+           IF WS-A = 100 OR WS-C = 99
+               DISPLAY 'OK: OR CONDITION'
+           ELSE
+               DISPLAY 'ERROR: OR'.
+           STOP RUN.

test-data/cobol/statement_control/ST-IF-DEEP.cbl

@@ -0,0 +1,24 @@
+      * ==== TYPE: ST-IF-DEEP ====
+      * FEATURE: IF nested 3+ levels deep
+      * STATEMENT: IF (nested)
+      * BRANCHES: 6, DECISIONS: 3
+       IDENTIFICATION DIVISION.
+       PROGRAM-ID. IFDEEP.
+       DATA DIVISION.
+       WORKING-STORAGE SECTION.
+       01 WS-X       PIC 9(1) VALUE 1.
+       01 WS-Y       PIC 9(1) VALUE 2.
+       01 WS-Z       PIC 9(1) VALUE 3.
+       PROCEDURE DIVISION.
+       MAIN.
+           IF WS-X = 1
+               IF WS-Y = 2
+                   IF WS-Z = 3
+                       DISPLAY 'OK: NESTED'
+                   ELSE
+                       DISPLAY 'ERR: Z'
+               ELSE
+                   DISPLAY 'ERR: Y'
+           ELSE
+               DISPLAY 'ERR: X'.
+           STOP RUN.