feat(api): initialize memoir chapter image assets on creation

Made-with: Cursor

api/tests/test_memoir_image_bootstrap.py

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+import unittest
+from unittest.mock import patch
+
+from api.tasks.memoir_tasks import initialize_chapter_images
+
+
+class MemoirImageBootstrapTest(unittest.TestCase):
+    @patch("api.tasks.memoir_tasks.generate_chapter_images.delay")
+    def test_initialize_chapter_images_sets_pending_assets_and_enqueues_task(self, delay_mock):
+        chapter = type(
+            "ChapterStub",
+            (),
+            {
+                "id": "chapter-1",
+                "title": "童年的夏天",
+                "category": "childhood",
+                "content": "那条路我一直记得。\n\n{{{{IMAGE:南方小镇的青石板路}}}}",
+                "images": [],
+            },
+        )()
+
+        assets = initialize_chapter_images(chapter)
+
+        self.assertEqual(len(assets), 1)
+        self.assertEqual(assets[0]["status"], "pending")
+        delay_mock.assert_called_once_with("chapter-1")