Add scan concurrency and login delay sliders

Serialised logins now sleep `login_delay` seconds between each SSH
auth to prevent AD/LDAP lockout. Both max sessions (1-10) and login
delay (0-15s) are configurable via UI sliders in the header and
passed as JSON to all scan endpoints.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scanner.py

@@ -26,7 +26,7 @@ scan_state = {
 }
 
 
-def run_scan(dept: str = None):
+def run_scan(dept: str = None, workers: int = 5, login_delay: int = 3):
     """
     Full scan: fetch switch IPs from NocoDB → SSH all → parse → store → export.
     dept: None = all active switches, "ELEC" or "GW" = dept-filtered.
@@ -105,7 +105,7 @@ def run_scan(dept: str = None):
                 "error": result.get("error", "Unknown error")
             })
 
-    scan_all_switches(switches, progress_callback=on_progress)
+    scan_all_switches(switches, progress_callback=on_progress, max_workers=workers, login_delay=login_delay)
 
     try:
         merge_duplicate_switches()