fix: alert panel always visible, version display normalization

- Remove x-show condition hiding alert panel when no alerts exist
- Add empty state message explaining alerts appear on rule triggers
- Normalize appVersion in loadVersion() to strip leading 'v' (prevents vv1.7.0 in footer)

backend/frontend/style.css

@@ -809,6 +809,15 @@ input {
   flex-wrap: wrap;
 }
 
+.alerts-empty {
+  padding: 20px;
+  text-align: center;
+  color: var(--muted);
+  font-size: 14px;
+  border: 1px dashed var(--border);
+  border-radius: 10px;
+}
+
 @media (max-width: 640px) {
   .topbar {
     flex-direction: column;