feat: add benchmark-programs — 58 telecom COBOL test programs

作为子目录纳入系统，与核心测试管道协同

Co-Authored-By: Claude <noreply@anthropic.com>

benchmark-programs/26-db-search/README.md

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+# 26-db-search — Database Search Simulation
+
+## 电信业务场景
+
+客户信息DB检索。使用索引文件模拟数据库检索，支持单键查询和范围查询，用于客户信息确认。
+
+## Purpose
+Simulates database search/retrieval patterns using GnuCOBOL INDEXED files with START + READ NEXT.
+
+## Test Coverage
+1. **Single key search** — READ with KEY IS for exact match retrieval
+2. **Range search** — START with NOT LESS THAN, iterate until upper bound
+3. **Full scan** — START from LOW-VALUES, read all records in key order
+4. **Range with no results** — START with no matching records
+
+## Key Techniques
+- INDEXED file with DYNAMIC access mode
+- START command for conditional positioning
+- READ NEXT for sequential traversal
+- KEY IS / GREATER THAN / NOT LESS THAN conditions
+- FILE STATUS checking