Reorganize task categories from opaque a/b to descriptive names

Replace category_a/category_b directories with algorithm, pipeline,
environment, filesystem, and process. Add separate mode field (solve/convert)
to decouple orchestration from capability grouping. Add per-category
summary and questionnaire breakdowns to both terminal report and HTML export.

lush_bench/agent.py

@@ -112,7 +112,7 @@ def solve_task(
     """Run the agent loop: prompt -> code -> test -> retry."""
     system = build_system_prompt(language)
 
-    if task.category == "b" and language == "lush":
+    if task.mode == "convert" and language == "lush":
         user_prompt = build_conversion_prompt(task)
     else:
         user_prompt = build_task_prompt(task, language)