feat(backend): persist tasks and generated message history

- add EntityTask domain and CRUD API backed by PostgreSQL

- relate generated messages directly to tasks and delete on task removal

- move preview generation to backend Llama endpoint

- migrate frontend task APIs from localStorage to backend endpoints

- update tests and CLAUDE rules for backend-owned LLM/persistence

backend/src/main/kotlin/com/condado/newsletter/model/EntityTask.kt

@@ -0,0 +1,53 @@
+package com.condado.newsletter.model
+
+import jakarta.persistence.CascadeType
+import jakarta.persistence.Column
+import jakarta.persistence.Entity
+import jakarta.persistence.FetchType
+import jakarta.persistence.GeneratedValue
+import jakarta.persistence.GenerationType
+import jakarta.persistence.Id
+import jakarta.persistence.JoinColumn
+import jakarta.persistence.ManyToOne
+import jakarta.persistence.OneToMany
+import jakarta.persistence.Table
+import org.hibernate.annotations.CreationTimestamp
+import java.time.LocalDateTime
+import java.util.UUID
+
+/**
+ * Represents a configurable task belonging to a virtual entity.
+ */
+@Entity
+@Table(name = "entity_tasks")
+class EntityTask(
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "entity_id", nullable = false)
+    val virtualEntity: VirtualEntity,
+
+    @Column(nullable = false)
+    val name: String,
+
+    @Column(columnDefinition = "TEXT", nullable = false)
+    val prompt: String,
+
+    @Column(name = "schedule_cron", nullable = false)
+    val scheduleCron: String,
+
+    @Column(name = "email_lookback", nullable = false)
+    val emailLookback: String,
+
+    @Column(nullable = false)
+    val active: Boolean = true,
+
+    @CreationTimestamp
+    @Column(name = "created_at", updatable = false, nullable = false)
+    val createdAt: LocalDateTime? = null
+) {
+    @Id
+    @GeneratedValue(strategy = GenerationType.UUID)
+    var id: UUID? = null
+
+    @OneToMany(mappedBy = "task", cascade = [CascadeType.ALL], orphanRemoval = true)
+    val generatedMessages: MutableList<GeneratedMessageHistory> = mutableListOf()
+}

backend/src/main/kotlin/com/condado/newsletter/model/GeneratedMessageHistory.kt

@@ -0,0 +1,37 @@
+package com.condado.newsletter.model
+
+import jakarta.persistence.Column
+import jakarta.persistence.Entity
+import jakarta.persistence.GeneratedValue
+import jakarta.persistence.GenerationType
+import jakarta.persistence.Id
+import jakarta.persistence.FetchType
+import jakarta.persistence.JoinColumn
+import jakarta.persistence.ManyToOne
+import jakarta.persistence.Table
+import java.time.LocalDateTime
+import java.util.UUID
+
+/**
+ * Stores generated test messages for a task, so the history survives page reloads and restarts.
+ */
+@Entity
+@Table(name = "generated_message_history")
+class GeneratedMessageHistory(
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "task_id", nullable = false)
+    val task: EntityTask,
+
+    @Column(nullable = false)
+    val label: String,
+
+    @Column(columnDefinition = "TEXT", nullable = false)
+    val content: String,
+
+    @Column(name = "created_at", nullable = false)
+    val createdAt: LocalDateTime = LocalDateTime.now()
+) {
+    @Id
+    @GeneratedValue(strategy = GenerationType.UUID)
+    var id: UUID? = null
+}