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>

PersonaEngine.psd1

@@ -53,6 +53,7 @@
         'Add-PersonaRunResult'
         'Test-PersonaReconciliation'
         'Get-PersonaReconciliationDetail'
+        'Export-PersonaResultsCsv'
         # Audit
         'New-PersonaAuditContext'
         'New-PersonaAuditRecord'