feat: add bounded business state observability

internal/storage/mysql/migrations/000026_operational_metrics.up.sql

@@ -0,0 +1,10 @@
+-- 为有界运行观测提供按状态和时间的前缀索引。
+-- 采集只读取固定状态的有限样本，不依赖外键或级联关系。
+ALTER TABLE pulse_tasks
+    ADD KEY ix_task_observe_state_available (state, available_at, id);
+
+ALTER TABLE orbit_deliveries
+    ADD KEY ix_delivery_observe_state_available (state, available_at, id);
+
+ALTER TABLE weave_instances
+    ADD KEY ix_workflow_observe_state_updated (state, updated_at, id);