feat: complete INSPECT/SEARCH support, fix PERFORM/EVAL coverage marking

- Add INSPECT (TALLYING/REPLACING/CONVERTING) with BEFORE/AFTER INITIAL
- Add SEARCH/SEARCH ALL with element-assignment path enumeration
- Fix _mark_perform compound condition marking via evaluate_tree
- Fix EVALUATE TRUE prior_false to collect all MC/DC false sets
- Add impossible path filtering (Pass A.5) with trace-to-root conflict detection
- Fix multi-line PERFORM VARYING parsing (VARYING/FROM/BY/UNTIL on separate lines)
- Remove dead code: agents.py LLM parser (replaced by rule-based _BrParser)
- 59 unit tests passing, 5 integration programs verified

cobol_testgen/read.py

@@ -52,7 +52,7 @@ def preprocess(source: str) -> str:
             if not line:
                 continue
             content = line
-        lines.append(content.upper())
+        lines.append(re.sub(r'\s+FALSE\s+[^\s.]+', '', content.upper()))
     return '\n'.join(lines)