fix: implement MO_USE_FIND and improve fd fallback logic

Fixes the issue reported in PR #410 where mo purge fails to find
artifacts when fd returns empty results.

Changes:
- Implement MO_USE_FIND environment variable to force using find
- Improve fd fallback: check if fd output is empty (-s test)
- Add debug logging to show which tool is being used
- If fd returns no results, fallback to find automatically

This fixes the root cause where fd successfully runs (exit 0) but
finds nothing, preventing the find fallback from being triggered.

scripts/setup-quick-launchers.sh

@@ -69,7 +69,7 @@ echo "🐹 Running ${title}..."
 echo ""
 
 # Command to execute
-_MO_RAW_CMD="${raw_cmd}"
+_MO_RAW_CMD='${raw_cmd}'
 _MO_CMD_ESCAPED="${cmd_escaped}"
 
 has_app() {