feat(alerting): AGENT_LIFECYCLE condition kind with per-subject fire mode

Allows alert rules to fire on agent-lifecycle events — REGISTERED,
RE_REGISTERED, DEREGISTERED, WENT_STALE, WENT_DEAD, RECOVERED — rather
than only on current state. Each matching `(agent, eventType, timestamp)`
becomes its own ackable AlertInstance, so outages on distinct agents are
independently routable.

Core:
- New `ConditionKind.AGENT_LIFECYCLE` + `AgentLifecycleCondition` record
  (scope, eventTypes, withinSeconds). Compact ctor rejects empty
  eventTypes and withinSeconds<1.
- Strict allowlist enum `AgentLifecycleEventType` (six entries matching
  the server-emitted types in `AgentRegistrationController` and
  `AgentLifecycleMonitor`). Custom agent-emitted event types tracked in
  backlog issue #145.
- `AgentEventRepository.findInWindow(env, appSlug, agentId, eventTypes,
  from, to, limit)` — new read path ordered `(timestamp ASC, insert_id
  ASC)` used by the evaluator. Implemented on
  `ClickHouseAgentEventRepository` with tenant + env filter mandatory.

App:
- `AgentLifecycleEvaluator` queries events in the last `withinSeconds`
  window and returns `EvalResult.Batch` with one `Firing` per row.
  Every Firing carries a canonical `_subjectFingerprint` of
  `"<agentId>:<eventType>:<tsMillis>"` in context plus `agent` / `event`
  subtrees for Mustache templating.
- `NotificationContextBuilder` gains an `AGENT_LIFECYCLE` branch that
  exposes `{{agent.id}}`, `{{agent.app}}`, `{{event.type}}`,
  `{{event.timestamp}}`, `{{event.detail}}`.
- Validation is delegated to the record compact ctor + enum at Jackson
  deserialization time — matches the existing policy of keeping
  controller validators focused on env-scoped / SQL-injection concerns.

Schema:
- V16 migration generalises the V15 per-exchange discriminator on
  `alert_instances_open_rule_uq` to prefer `_subjectFingerprint` with a
  fallback to the legacy `exchange.id` expression. Scalar kinds still
  resolve to `''` and keep one-open-per-rule. Duplicate-key path in
  `PostgresAlertInstanceRepository.save` is unchanged — the index is
  the deduper.

UI:
- New `AgentLifecycleForm.tsx` wizard form with multi-select chips for
  the six allowed event types + `withinSeconds` input. Wired into
  `ConditionStep`, `form-state` (validation + defaults: WENT_DEAD,
  300 s), and `enums.ts` options. Tests in `enums.test.ts` pin the
  new option array.
- `alert-variables.ts` registers `{{agent.app}}`, `{{event.type}}`,
  `{{event.timestamp}}`, `{{event.detail}}` leaves for the new kind,
  and extends `agent.id`'s availability list to include `AGENT_LIFECYCLE`.

Tests (all passing):
- 5 new JSON-roundtrip cases on `AlertConditionJsonTest` (positive +
  empty/zero/unknown-type rejection).
- 5 new evaluator unit tests on `AgentLifecycleEvaluatorTest` (empty
  window, multi-agent fingerprint shape, scope forwarding, missing env).
- `NotificationContextBuilderTest` switch now covers the new kind.
- 119 alerting unit tests + 71 UI tests green.

Docs: `.claude/rules/{core,app,ui}` and CLAUDE.md migration list updated.

cameleer-server-app/src/main/resources/db/migration/V16__alert_instances_subject_fingerprint.sql

@@ -0,0 +1,27 @@
+-- V16 — Generalise open-alert_instance uniqueness via `_subjectFingerprint`.
+--
+-- V15 discriminated open instances by `context->'exchange'->>'id'` so that
+-- EXCHANGE_MATCH / PER_EXCHANGE could emit one instance per exchange. The new
+-- AGENT_LIFECYCLE / PER_AGENT condition has the same shape but a different
+-- subject key (agentId + eventType + eventTs). Rather than bolt condition-kind
+-- knowledge into the index, we introduce a canonical `_subjectFingerprint`
+-- field in `context` that every "per-subject" evaluator writes. The index
+-- prefers it over the legacy exchange.id discriminator.
+--
+-- Precedence in the COALESCE:
+--   1. context->>'_subjectFingerprint'  — explicit per-subject key (new)
+--   2. context->'exchange'->>'id'       — legacy EXCHANGE_MATCH instances (pre-V16)
+--   3. ''                                — scalar condition kinds (one open per rule)
+--
+-- Existing open PER_EXCHANGE instances keep working because they never set
+-- `_subjectFingerprint` but do carry `context.exchange.id`, so the index
+-- still discriminates them correctly.
+DROP INDEX IF EXISTS alert_instances_open_rule_uq;
+
+CREATE UNIQUE INDEX alert_instances_open_rule_uq
+  ON alert_instances (rule_id, (COALESCE(
+        context->>'_subjectFingerprint',
+        context->'exchange'->>'id',
+        '')))
+  WHERE rule_id IS NOT NULL
+    AND state IN ('PENDING','FIRING','ACKNOWLEDGED');