feat: alert rules management UI

- Add Alert Rules panel between Alerts and Filters sections
- List all rules with severity badge, on/off toggle, conditions preview
- Add Rule button opens modal with form for name, severity, message, conditions
- Edit existing rules inline
- Delete rules with confirmation
- Condition builder supports eq, neq, contains, in, after_hours operators

backend/frontend/style.css

@@ -818,6 +818,130 @@ input {
   border-radius: 10px;
 }
 
+/* Rules management */
+.rules-list {
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+}
+
+.rule-card {
+  border: 1px solid var(--border);
+  border-radius: 12px;
+  padding: 12px 14px;
+  background: rgba(255, 255, 255, 0.02);
+}
+
+.rule-card--disabled {
+  opacity: 0.6;
+}
+
+.rule-card__meta {
+  display: flex;
+  gap: 8px;
+  align-items: center;
+  margin-bottom: 6px;
+  flex-wrap: wrap;
+}
+
+.toggle-label {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  font-size: 12px;
+  color: var(--muted);
+  cursor: pointer;
+}
+
+.toggle-label input[type="checkbox"] {
+  width: 14px;
+  height: 14px;
+  accent-color: var(--accent-strong);
+}
+
+.rule-card strong {
+  font-size: 14px;
+  display: block;
+  margin-bottom: 4px;
+}
+
+.rule-card p {
+  margin: 0 0 8px;
+  font-size: 13px;
+  color: var(--muted);
+  line-height: 1.4;
+}
+
+.rule-card__conditions {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 6px;
+  margin-bottom: 10px;
+}
+
+.rule-card__actions {
+  display: flex;
+  gap: 8px;
+}
+
+.rules-empty {
+  padding: 20px;
+  text-align: center;
+  color: var(--muted);
+  font-size: 14px;
+  border: 1px dashed var(--border);
+  border-radius: 10px;
+}
+
+.rule-form {
+  display: flex;
+  flex-direction: column;
+  gap: 14px;
+}
+
+.rule-form label {
+  display: flex;
+  flex-direction: column;
+  gap: 6px;
+  font-size: 14px;
+  color: var(--muted);
+}
+
+.rule-form input,
+.rule-form select,
+.rule-form textarea {
+  padding: 10px 12px;
+  border-radius: 10px;
+  border: 1px solid var(--border);
+  background: rgba(255, 255, 255, 0.02);
+  color: var(--text);
+  font-size: 14px;
+}
+
+.rule-conditions {
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+}
+
+.condition-row {
+  display: flex;
+  gap: 8px;
+  align-items: center;
+}
+
+.condition-row input,
+.condition-row select {
+  flex: 1;
+  min-width: 0;
+}
+
+.rule-form__actions {
+  display: flex;
+  gap: 10px;
+  margin-top: 8px;
+}
+
 @media (max-width: 640px) {
   .topbar {
     flex-direction: column;