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-app/src/main/resources/db/migration/V14__fix_null_firemode_alert_rules.sql

@@ -0,0 +1,19 @@
+-- V14 — Repair EXCHANGE_MATCH rules persisted with fireMode=null.
+-- Root cause: the rule editor wizard reset the condition payload on kind
+-- change without seeding a fireMode default, and the backend ctor allowed
+-- null to pass. Stricter ctor in ExchangeMatchCondition now rejects null
+-- fireMode — existing rows need to be repaired so startup doesn't fail
+-- deserialization and the evaluator stops NPE-looping on them.
+--
+-- Default to PER_EXCHANGE + perExchangeLingerSeconds=300 — the same default
+-- the UI now seeds when a user picks EXCHANGE_MATCH.
+UPDATE alert_rules
+   SET condition = jsonb_set(
+                     jsonb_set(condition, '{fireMode}', '"PER_EXCHANGE"', true),
+                     '{perExchangeLingerSeconds}',
+                     COALESCE(condition->'perExchangeLingerSeconds', '300'::jsonb),
+                     true
+                   ),
+       updated_at = now()
+ WHERE condition_kind = 'EXCHANGE_MATCH'
+   AND (condition->>'fireMode') IS NULL;