Add elapsed run time, per-account results CSV, and a default config path

Summaries now show elapsed wall-clock time since the run started, and every
summary (interim and final) overwrites a results.csv (Object ID, UPN,
persona/status) next to the audit log, so an operator has a plain export
without parsing NDJSON. ConfigPath also now defaults to
./config/persona-engine.json instead of requiring -ConfigPath every run.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

config/persona-engine.example.json

@@ -26,6 +26,7 @@
   },
   "logging": {
     "destination": "both",
+    "resultsFileName": "results.csv",
     "traceConditionValues": false
   },
   "personas": [