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": [

config/persona-engine.schema.json

@@ -105,6 +105,12 @@
           "type": "string",
           "description": "NDJSON output file for 'file'/'both' destinations. Defaults to <current-directory>/logs/persona-engine-audit.ndjson when unset."
         },
+        "resultsFileName": {
+          "type": "string",
+          "minLength": 1,
+          "default": "results.csv",
+          "description": "Per-account results CSV (AccountObjectId, UserPrincipalName, persona/status), written alongside the audit log and overwritten on every summary."
+        },
         "traceConditionValues": {
           "type": "boolean",
           "default": false,