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.

tasks/algorithm/reverse_string.toml

@@ -0,0 +1,22 @@
+name = "reverse_string"
+category = "algorithm"
+mode = "solve"
+description = """
+Read a single line from stdin and print it reversed to stdout.
+"""
+
+[[test_cases]]
+stdin = "hello"
+expected_stdout = "olleh"
+
+[[test_cases]]
+stdin = "abcdef"
+expected_stdout = "fedcba"
+
+[[test_cases]]
+stdin = "racecar"
+expected_stdout = "racecar"
+
+[[test_cases]]
+stdin = "a"
+expected_stdout = "a"