fix(alerting): reject null fireMode on ExchangeMatchCondition + repair in-flight rows

The rule editor wizard reset the condition payload on kind-change without
seeding a fireMode default; the ExchangeMatchCondition ctor allowed null to
pass through; AlertEvaluatorJob then NPE-looped every tick on a saved rule.

- core: compact ctor now rejects null fireMode (Jackson-deser path only — all
  production callers already pass a value).
- V14: repair existing EXCHANGE_MATCH rows with fireMode=null to
  PER_EXCHANGE + perExchangeLingerSeconds=300 (default matches the wizard).
- ui: ConditionStep.onKindChange seeds EXCHANGE_MATCH defaults so the
  Select's displayed fallback ("Per exchange") is actually in form state.
- ui: validateStep('condition', ...) now enforces fireMode presence + the
  mode-specific fields before the user reaches Review.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

cameleer-server-core/src/main/java/com/cameleer/server/core/alerting/ExchangeMatchCondition.java

@@ -14,6 +14,8 @@ public record ExchangeMatchCondition(
 ) implements AlertCondition {
 
     public ExchangeMatchCondition {
+        if (fireMode == null)
+            throw new IllegalArgumentException("fireMode is required (PER_EXCHANGE or COUNT_IN_WINDOW)");
         if (fireMode == FireMode.COUNT_IN_WINDOW && (threshold == null || windowSeconds == null))
             throw new IllegalArgumentException("COUNT_IN_WINDOW requires threshold + windowSeconds");
         if (fireMode == FireMode.PER_EXCHANGE && perExchangeLingerSeconds == null)

cameleer-server-core/src/test/java/com/cameleer/server/core/alerting/AlertConditionJsonTest.java

@@ -6,6 +6,7 @@ import java.util.List;
 import java.util.Map;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
 class AlertConditionJsonTest {
 
@@ -43,6 +44,34 @@ class AlertConditionJsonTest {
         assertThat(((ExchangeMatchCondition) parsed).threshold()).isEqualTo(5);
     }
 
+    @Test
+    void exchangeMatchRejectsNullFireMode() {
+        assertThatThrownBy(() -> new ExchangeMatchCondition(
+                new AlertScope(null, null, null),
+                new ExchangeMatchCondition.ExchangeFilter("FAILED", Map.of()),
+                null, null, null, null))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("fireMode");
+    }
+
+    @Test
+    void exchangeMatchRejectsNullFireModeOnDeserialization() throws Exception {
+        String json = """
+            {
+              "kind": "EXCHANGE_MATCH",
+              "scope": {},
+              "filter": {"status": "FAILED", "attributes": {}},
+              "fireMode": null,
+              "threshold": null,
+              "windowSeconds": null,
+              "perExchangeLingerSeconds": null
+            }
+            """;
+        assertThatThrownBy(() -> om.readValue(json, AlertCondition.class))
+            .hasRootCauseInstanceOf(IllegalArgumentException.class)
+            .hasMessageContaining("fireMode");
+    }
+
     @Test
     void roundtripAgentState() throws Exception {
         var c = new AgentStateCondition(new AlertScope("orders", null, null), "DEAD", 60);