test(ai): add 25-query benchmark harness + results for ai mode models

Adds a repeatable AI-mode benchmark (ai-benchmark.sh) covering 25 queries across
8 categories and 3 difficulty tiers, plus captured latency results and manual
correctness grades for qwen2.5-coder:1.5b, qwen2.5:3b, and westenfelder/NL2SH.

Headline finding: on the larger suite NL2SH is most accurate (72% vs coder 40%,
3b 32%) and the only model with non-zero hard-task accuracy (50% vs coder 0%),
while qwen2.5-coder is ~2x faster (median 3.0s vs 6.3s). This reverses the
earlier 7-query result that favored qwen-coder overall.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/performance/ai-benchmark.sh

@@ -0,0 +1,73 @@
+#!/bin/bash
+# AI mode benchmark harness for super-man.
+# Runs a fixed query suite against each model and records latency + the
+# generated command to a pipe-delimited CSV for analysis/reporting.
+#
+# Usage: ./ai-benchmark.sh [model1 model2 ...]
+# Default models: qwen2.5-coder:1.5b qwen2.5:3b westenfelder/NL2SH
+#
+# Output: tests/performance/ai-results.csv  (model|id|category|difficulty|query|latency_s|command)
+
+set -u
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+SUPERMAN="$SCRIPT_DIR/../../super-man.sh"
+OUT="$SCRIPT_DIR/ai-results.csv"
+
+MODELS=("$@")
+if [ ${#MODELS[@]} -eq 0 ]; then
+  MODELS=("qwen2.5-coder:1.5b" "qwen2.5:3b" "westenfelder/NL2SH")
+fi
+
+# Suite: id|category|difficulty|query
+SUITE=(
+  "q01|files|easy|list the 5 largest files in the current directory"
+  "q02|files|easy|show hidden files in long format"
+  "q03|files|medium|find files larger than 100MB under the home directory"
+  "q04|files|medium|recursively change permissions of all directories to 755"
+  "q05|files|hard|find duplicate files by content in the current tree"
+  "q06|text|easy|count the number of lines in all python files"
+  "q07|text|medium|replace all tabs with two spaces in config.txt in place"
+  "q08|text|medium|print the 10 most common words in access.log"
+  "q09|text|hard|sum the numbers in the third column of data.csv"
+  "q10|search|easy|recursively search for the word TODO in all js files"
+  "q11|search|medium|find files modified in the last 24 hours"
+  "q12|search|hard|find python files that import requests but not os"
+  "q13|process|easy|show the top 10 processes by memory usage"
+  "q14|process|medium|kill the process listening on port 8080"
+  "q15|process|hard|show the total cpu time used by all chrome processes"
+  "q16|network|easy|download a file from a url and save it as out.bin"
+  "q17|network|medium|list all open listening tcp ports with the owning process"
+  "q18|network|hard|test whether port 443 is open on example.com"
+  "q19|archive|easy|compress the folder logs into a gzip tarball"
+  "q20|archive|medium|extract only txt files from archive.tar.gz"
+  "q21|system|easy|show disk usage of the current directory in human readable form"
+  "q22|system|medium|show the 5 largest directories under /var"
+  "q23|git|easy|show the last 5 git commits in one line each"
+  "q24|git|medium|list files changed in the last commit"
+  "q25|git|hard|find the commit that introduced the string getUserById"
+)
+
+strip() { sed -E 's/\x1b\[[0-9;]*m//g'; }
+
+echo "model|id|category|difficulty|query|latency_s|command" > "$OUT"
+
+for m in "${MODELS[@]}"; do
+  echo ">> Warming up $m ..."
+  ollama run "$m" "echo hi" >/dev/null 2>&1
+  echo ">> Benchmarking $m (${#SUITE[@]} queries)"
+  for row in "${SUITE[@]}"; do
+    IFS='|' read -r id cat diff q <<< "$row"
+    start=$(date +%s.%N)
+    cmd=$("$SUPERMAN" ai --model "$m" "$q" 2>&1 | strip \
+          | awk '/Generated Command:/{getline; gsub(/^[[:space:]]+/,""); print; exit}')
+    end=$(date +%s.%N)
+    el=$(awk "BEGIN{printf \"%.2f\", $end-$start}")
+    # squash any embedded pipes/newlines in the captured command for CSV safety
+    cmd=$(printf '%s' "$cmd" | tr '\n' ' ' | sed 's/|/¦/g')
+    printf "%s|%s|%s|%s|%s|%s|%s\n" "$m" "$id" "$cat" "$diff" "$q" "$el" "$cmd" >> "$OUT"
+    printf "  [%s] %-5s %5ss  %s\n" "$m" "$id" "$el" "$cmd"
+  done
+done
+
+echo ""
+echo "Done -> $OUT"