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/fizzbuzz.toml

@@ -1,5 +1,6 @@
 name = "fizzbuzz"
-category = "a"
+category = "algorithm"
+mode = "solve"
 description = """
 Read a single integer N from stdin. Print numbers from 1 to N, one per line.
 For multiples of 3, print "Fizz" instead of the number.

tasks/algorithm/reverse_string.toml

@@ -1,5 +1,6 @@
 name = "reverse_string"
-category = "a"
+category = "algorithm"
+mode = "solve"
 description = """
 Read a single line from stdin and print it reversed to stdout.
 """

tasks/algorithm/two_sum.toml

@@ -1,5 +1,6 @@
 name = "two_sum"
-category = "a"
+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).

tasks/environment/env_config.toml

@@ -1,5 +1,6 @@
 name = "env_config"
-category = "a"
+category = "environment"
+mode = "solve"
 description = """
 Read a config format from stdin where each line is "KEY=VALUE".
 For each line, set an environment variable with that key and value.

tasks/environment/env_path_builder.toml

@@ -1,5 +1,6 @@
 name = "env_path_builder"
-category = "b"
+category = "environment"
+mode = "convert"
 description = """
 Read directory paths from stdin, one per line.
 Append each to the MYPATH environment variable (colon-separated), skipping duplicates.

tasks/filesystem/file_organizer.toml

@@ -1,5 +1,6 @@
 name = "file_organizer"
-category = "a"
+category = "filesystem"
+mode = "solve"
 description = """
 You are given a working directory containing several files with extensions.
 Read a list of extension-to-directory mappings from stdin, one per line, in the format:

tasks/filesystem/multi_file_search.toml

@@ -1,5 +1,6 @@
 name = "multi_file_search"
-category = "a"
+category = "filesystem"
+mode = "solve"
 description = """
 You are given a working directory containing several text files.
 Read a search pattern (a simple string, not regex) from stdin.

tasks/pipeline/csv_transform.toml

@@ -1,5 +1,6 @@
 name = "csv_transform"
-category = "b"
+category = "pipeline"
+mode = "convert"
 description = """
 Read CSV data from stdin. The first line is a header.
 Each subsequent line has fields: name,age,city

tasks/pipeline/log_parser.toml

@@ -1,5 +1,6 @@
 name = "log_parser"
-category = "b"
+category = "pipeline"
+mode = "convert"
 description = """
 Read log lines from stdin. Each line has the format: "LEVEL: message"
 where LEVEL is one of ERROR, WARN, INFO.

tasks/pipeline/pipeline_transform.toml

@@ -1,5 +1,6 @@
 name = "pipeline_transform"
-category = "a"
+category = "pipeline"
+mode = "solve"
 description = """
 Read lines from stdin. Build a pipeline that:
 1. Filters to only lines containing the word "error" (case-insensitive)

tasks/pipeline/pipeline_word_freq.toml

@@ -1,5 +1,6 @@
 name = "pipeline_word_freq"
-category = "b"
+category = "pipeline"
+mode = "convert"
 description = """
 Read text from stdin. Count the frequency of each word (case-insensitive, only alphabetic characters count as words).
 Print the top 5 most frequent words in descending order of frequency, in the format:

tasks/process/process_exit_codes.toml

@@ -1,5 +1,6 @@
 name = "process_exit_codes"
-category = "a"
+category = "process"
+mode = "solve"
 description = """
 Read commands from stdin, one per line. Execute each command as a subprocess.
 For each command, print: "command: exit_code" where command is the original command text