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_inspect/ST-INSP-CONVERT.cbl

@@ -0,0 +1,20 @@
+      * ==== TYPE: ST-INSP-CONVERT ====
+      * FEATURE: INSPECT CONVERTING + TALLYING
+      * STATEMENT: INSPECT
+      * BRANCHES: 2, DECISIONS: 1
+       IDENTIFICATION DIVISION.
+       PROGRAM-ID. INSCNV.
+       DATA DIVISION.
+       WORKING-STORAGE SECTION.
+       01 WS-TEXT    PIC X(15) VALUE 'abc-123-def-456'.
+       01 WS-CNT     PIC 9(3) VALUE 0.
+       01 WS-TALLY   PIC 9(3) VALUE 0.
+       PROCEDURE DIVISION.
+       MAIN.
+           INSPECT WS-TEXT CONVERTING 'abcdef' TO 'ABCDEF'.
+           INSPECT WS-TEXT TALLYING WS-TALLY FOR ALL '-'.
+           IF WS-TALLY = 3
+               DISPLAY 'OK: INSPECT'
+           ELSE
+               DISPLAY 'ERROR: INSPECT'.
+           STOP RUN.