Enhance launcher shebang polyglot to fall back to Bun if Node is missing on the system

Result: {"status":"keep","test_status":0}

autoresearch.jsonl

@@ -1,2 +1,3 @@
 {"type":"config","name":"Fixing Windows execution wrapper regression by rewriting launcher in Node.js","metricName":"test_status","metricUnit":"","bestDirection":"lower"}
 {"run":1,"commit":"65b813d","metric":0,"metrics":{},"status":"keep","description":"Rewrite launcher in Node.js to fix Windows execution and keep tests passing","timestamp":1779480224809,"segment":0,"confidence":null,"asi":{"hypothesis":"Rewrite launcher in Node.js to enable native cmd/ps1 wrappers on Windows, and adjust mock node in tests to delegate wrapper execution"}}
+{"run":2,"commit":"7a5d8f5","metric":0,"metrics":{},"status":"keep","description":"Make bin/qmd launcher a shebang polyglot to support both Windows cmd/ps1 native wrappers and sh-invoked smoke tests","timestamp":1779480529550,"segment":0,"confidence":null,"asi":{"hypothesis":"Convert launcher to a polyglot shell/JS script starting with #!/usr/bin/env node, and fix JS falsy env-var evaluation to support package-smoke tests"}}

bin/qmd

@@ -1,5 +1,5 @@
 #!/usr/bin/env node
-// 2>/dev/null; exec node "$0" "$@"
+// 2>/dev/null; if command -v node >/dev/null 2>&1; then exec node "$0" "$@"; else exec bun "$0" "$@"; fi
 // Cross-platform launcher for qmd.
 //
 // Previously this was a POSIX shell script with `#!/bin/sh`, which meant npm