Fix scan log dismiss button visibility and truncate error messages

Dismiss button is now always visible with a bordered style instead of
hidden-until-JS. Netmiko error messages are truncated to first line
(120 chars) so verbose multi-line errors don't flood the log panel.

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

scanner.py

@@ -112,9 +112,10 @@ def run_scan(dept: str = None, workers: int = 5, login_delay: int = 3):
             scan_state["fail"] += 1
             error = result.get("error", "Unknown error")
             scan_state["errors"].append({"ip": ip, "error": error})
+            error_short = error.splitlines()[0][:120]
             scan_state["log_lines"].append({
                 "ts": ts, "ok": False,
-                "text": f"✗  {ip}  — {error}",
+                "text": f"✗  {ip}  — {error_short}",
             })
 
     scan_all_switches(switches, progress_callback=on_progress, max_workers=workers, login_delay=login_delay)