Merge tasks into notes: a task is just a note with task attributes

A task is now a note with status/priority/due_date columns set (status IS NOT NULL).
This eliminates the separate tasks table, companion note system, cascade deletes,
bidirectional title sync, and _skip_cascade flags.

Migration (0004):
- Add status, priority, due_date columns to notes table
- Migrate task data from companion notes and orphan tasks
- Drop tasks table and old enum types

Backend:
- models/note.py: Add TaskStatus/TaskPriority enums, task columns, is_task property
- models/task.py: Deleted (merged into note.py)
- models/__init__.py: Re-export enums from note.py, remove Task import
- services/notes.py: Remove companion/cascade logic, add is_task filter,
  convert_note_to_task, convert_task_to_note, simplified backlinks
- services/tasks.py: Rewritten as thin wrappers around notes service
- routes/notes.py: Add is_task filter (default false), task fields in CRUD,
  convert-to-note endpoint
- routes/tasks.py: description→body (with fallback), remove note_id filter

Frontend:
- types/note.ts: Add TaskStatus, TaskPriority, task fields to Note interface
- types/task.ts: Task is now a re-export alias for Note
- stores/notes.ts: Simplify convertToTask, add convertToNote
- stores/tasks.ts: description→body in createTask/updateTask
- TaskEditorView: description→body, remove companion note UI
- TaskViewerView: description→body, remove companion note link, add Convert to Note
- NoteViewerView: Remove companion task UI, simplify convert-to-task
- TaskCard: description→body, non-null assertions for status/priority

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/views/TaskViewerView.vue

@@ -5,7 +5,7 @@ import { useTasksStore } from "@/stores/tasks";
 import { useNotesStore } from "@/stores/notes";
 import { renderMarkdown } from "@/utils/markdown";
 import { relativeTime } from "@/composables/useRelativeTime";
-import { apiGet, apiPost } from "@/api/client";
+import { apiPost } from "@/api/client";
 import type { Note } from "@/types/note";
 import type { TaskStatus } from "@/types/task";
 import StatusBadge from "@/components/StatusBadge.vue";
@@ -16,28 +16,18 @@ const route = useRoute();
 const router = useRouter();
 const store = useTasksStore();
 const notesStore = useNotesStore();
-const linkedNote = ref<Note | null>(null);
 const backlinks = ref<{ type: string; id: number; title: string }[]>([]);
+const converting = ref(false);
 
 const taskId = computed(() => Number(route.params.id));
 
 async function loadTask(id: number) {
-  linkedNote.value = null;
   backlinks.value = [];
   await store.fetchTask(id);
-  if (store.currentTask?.note_id) {
-    try {
-      linkedNote.value = await apiGet<Note>(
-        `/api/notes/${store.currentTask.note_id}`
-      );
-    } catch {
-      linkedNote.value = null;
-    }
-    try {
-      backlinks.value = await notesStore.fetchBacklinks(store.currentTask.note_id);
-    } catch {
-      backlinks.value = [];
-    }
+  try {
+    backlinks.value = await notesStore.fetchBacklinks(id);
+  } catch {
+    backlinks.value = [];
   }
 }
 
@@ -47,9 +37,9 @@ watch(() => route.params.id, (newId) => {
   if (newId) loadTask(Number(newId));
 });
 
-const renderedDescription = computed(() => {
+const renderedBody = computed(() => {
   if (!store.currentTask) return "";
-  return renderMarkdown(store.currentTask.description);
+  return renderMarkdown(store.currentTask.body);
 });
 
 const statusCycle: Record<TaskStatus, TaskStatus> = {
@@ -62,7 +52,7 @@ function cycleStatus() {
   if (!store.currentTask) return;
   store.patchStatus(
     store.currentTask.id,
-    statusCycle[store.currentTask.status]
+    statusCycle[store.currentTask.status as TaskStatus]
   );
 }
 
@@ -74,6 +64,22 @@ function isOverdue(): boolean {
   );
 }
 
+async function convertToNote() {
+  if (converting.value) return;
+  converting.value = true;
+  try {
+    await notesStore.convertToNote(taskId.value);
+    const { useToastStore } = await import("@/stores/toast");
+    useToastStore().show("Converted to note");
+    router.push(`/notes/${taskId.value}`);
+  } catch {
+    const { useToastStore } = await import("@/stores/toast");
+    useToastStore().show("Failed to convert task", "error");
+  } finally {
+    converting.value = false;
+  }
+}
+
 async function onBodyClick(e: MouseEvent) {
   const target = e.target as HTMLElement;
 
@@ -123,6 +129,13 @@ function onTagClick(tag: string) {
         >
           Edit
         </router-link>
+        <button
+          class="btn-convert"
+          @click="convertToNote"
+          :disabled="converting"
+        >
+          {{ converting ? "Converting..." : "Convert to Note" }}
+        </button>
       </div>
       <h1>{{ store.currentTask.title || "Untitled" }}</h1>
       <p class="meta">
@@ -132,11 +145,11 @@ function onTagClick(tag: string) {
       </p>
       <div class="badges">
         <StatusBadge
-          :status="store.currentTask.status"
+          :status="store.currentTask.status!"
           clickable
           @click="cycleStatus"
         />
-        <PriorityBadge :priority="store.currentTask.priority" />
+        <PriorityBadge :priority="store.currentTask.priority!" />
         <span
           v-if="store.currentTask.due_date"
           :class="['due-date', { overdue: isOverdue() }]"
@@ -144,14 +157,6 @@ function onTagClick(tag: string) {
           Due: {{ store.currentTask.due_date }}
         </span>
       </div>
-      <div
-        v-if="linkedNote"
-        class="linked-note"
-      >
-        <router-link :to="`/notes/${linkedNote.id}`" class="note-link">
-          View Note
-        </router-link>
-      </div>
       <div class="tags" v-if="store.currentTask.tags.length">
         <TagPill
           v-for="tag in store.currentTask.tags"
@@ -162,7 +167,7 @@ function onTagClick(tag: string) {
       </div>
       <div
         class="body prose"
-        v-html="renderedDescription"
+        v-html="renderedBody"
         @click="onBodyClick"
       ></div>
 
@@ -201,6 +206,25 @@ function onTagClick(tag: string) {
   text-decoration: none;
   color: var(--color-primary);
 }
+.btn-convert {
+  margin-left: auto;
+  padding: 0.3rem 0.75rem;
+  background: var(--color-bg-secondary);
+  color: var(--color-text);
+  border: 1px solid var(--color-border);
+  border-radius: 4px;
+  cursor: pointer;
+  font-size: 0.85rem;
+}
+.btn-convert:hover {
+  background: var(--color-primary);
+  color: #fff;
+  border-color: var(--color-primary);
+}
+.btn-convert:disabled {
+  opacity: 0.6;
+  cursor: default;
+}
 .meta {
   font-size: 0.85rem;
   color: var(--color-text-muted);
@@ -220,18 +244,6 @@ function onTagClick(tag: string) {
   color: var(--color-overdue);
   font-weight: 600;
 }
-.linked-note {
-  font-size: 0.9rem;
-  color: var(--color-text-secondary);
-  margin-bottom: 0.75rem;
-}
-.note-link {
-  color: var(--color-primary);
-  text-decoration: none;
-}
-.note-link:hover {
-  text-decoration: underline;
-}
 .tags {
   display: flex;
   gap: 0.5rem;