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

frontend/src/pages/EditTaskPage.tsx

@@ -1,12 +1,14 @@
-import { useEffect, useMemo, useRef, useState } from 'react'
+import { useEffect, useMemo, useState } from 'react'
 import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query'
 import { Link, useNavigate, useParams } from 'react-router-dom'
 import { getEntity } from '../api/entitiesApi'
 import {
   activateTask,
   buildTaskPreviewPrompt,
+  deleteTaskGeneratedMessage,
   deleteTask,
   generateTaskPreview,
+  getTaskGeneratedMessages,
   getTask,
   inactivateTask,
   updateTask,
@@ -35,12 +37,6 @@ interface RegularitySuggestion {
   cronParts: CronParts
 }
 
-interface GeneratedMessageItem {
-  id: string
-  label: string
-  content: string
-}
-
 const DEFAULT_CRON_PARTS: CronParts = {
   minute: '0',
   hour: '9',
@@ -121,10 +117,8 @@ export default function EditTaskPage() {
   const queryClient = useQueryClient()
   const [cronParts, setCronParts] = useState<CronParts>(DEFAULT_CRON_PARTS)
   const [taskForm, setTaskForm] = useState<TaskFormState>(DEFAULT_TASK_FORM)
-  const [generatedMessages, setGeneratedMessages] = useState<GeneratedMessageItem[]>([])
   const [selectedMessageId, setSelectedMessageId] = useState('')
   const [previewError, setPreviewError] = useState('')
-  const generatedMessageCounter = useRef(0)
 
   const { data: entity, isLoading: isLoadingEntity } = useQuery({
     queryKey: ['entity', entityId],
@@ -138,6 +132,26 @@ export default function EditTaskPage() {
     enabled: Boolean(taskId),
   })
 
+  const { data: generatedMessages = [] } = useQuery({
+    queryKey: ['task-generated-messages', taskId],
+    queryFn: () => getTaskGeneratedMessages(taskId),
+    enabled: Boolean(taskId),
+  })
+
+  useEffect(() => {
+    if (generatedMessages.length === 0) {
+      if (selectedMessageId) {
+        setSelectedMessageId('')
+      }
+      return
+    }
+
+    const hasCurrentSelection = generatedMessages.some((message) => message.id === selectedMessageId)
+    if (!hasCurrentSelection) {
+      setSelectedMessageId(generatedMessages[0].id)
+    }
+  }, [generatedMessages, selectedMessageId])
+
   useEffect(() => {
     if (!task) {
       return
@@ -193,20 +207,13 @@ export default function EditTaskPage() {
   })
 
   const previewMutation = useMutation({
-    mutationFn: generateTaskPreview,
+    mutationFn: (payload: Parameters<typeof generateTaskPreview>[1]) =>
+      generateTaskPreview(taskId, payload),
     onMutate: () => {
       setPreviewError('')
     },
-    onSuccess: (value) => {
-      generatedMessageCounter.current += 1
-      const nextMessage: GeneratedMessageItem = {
-        id: `message-${generatedMessageCounter.current}`,
-        label: `Message #${generatedMessageCounter.current}`,
-        content: value,
-      }
-
-      setGeneratedMessages((prev) => [nextMessage, ...prev])
-      setSelectedMessageId(nextMessage.id)
+    onSuccess: async () => {
+      await queryClient.invalidateQueries({ queryKey: ['task-generated-messages', taskId] })
     },
     onError: (error) => {
       setPreviewError(
@@ -246,6 +253,13 @@ export default function EditTaskPage() {
     [generatedMessages, selectedMessageId]
   )
 
+  const deleteGeneratedMessageMutation = useMutation({
+    mutationFn: (messageId: string) => deleteTaskGeneratedMessage(taskId, messageId),
+    onSuccess: async () => {
+      await queryClient.invalidateQueries({ queryKey: ['task-generated-messages', taskId] })
+    },
+  })
+
   const applyCronParts = (nextCronParts: CronParts) => {
     setCronParts(nextCronParts)
     setTaskForm((prev) => ({ ...prev, scheduleCron: buildCron(nextCronParts) }))
@@ -514,13 +528,7 @@ export default function EditTaskPage() {
                       <button
                         type="button"
                         onClick={() => {
-                          setGeneratedMessages((prev) => {
-                            const nextMessages = prev.filter((item) => item.id !== message.id)
-                            if (selectedMessageId === message.id) {
-                              setSelectedMessageId(nextMessages[0]?.id ?? '')
-                            }
-                            return nextMessages
-                          })
+                          deleteGeneratedMessageMutation.mutate(message.id)
                         }}
                         className="rounded border border-red-500/40 px-2 py-1 text-[10px] font-semibold uppercase tracking-wide text-red-300 hover:bg-red-500/10"
                         aria-label={`Delete ${message.label.toLowerCase()}`}