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/two_sum.toml

@@ -0,0 +1,25 @@
+name = "two_sum"
+category = "algorithm"
+mode = "solve"
+description = """
+Read input from stdin. The first line contains a target integer.
+The second line contains space-separated integers (the array).
+Find two indices (0-based) such that the numbers at those indices add up to the target.
+Print the two indices on a single line, space-separated, smaller index first.
+There is exactly one solution.
+"""
+
+[[test_cases]]
+stdin = """9
+2 7 11 15"""
+expected_stdout = "0 1"
+
+[[test_cases]]
+stdin = """6
+3 2 4"""
+expected_stdout = "1 2"
+
+[[test_cases]]
+stdin = """6
+3 3"""
+expected_stdout = "0 1"