feat(api): add memoir image prompt settings and optimization service

Made-with: Cursor

api/tests/test_memoir_image_prompting.py

@@ -0,0 +1,59 @@
+import unittest
+from unittest.mock import Mock
+
+from api.services.memoir_images.prompting import MemoirImagePromptService
+from api.services.memoir_images.settings import MemoirImageSettings
+
+
+class MemoirImagePromptingTest(unittest.TestCase):
+    def test_prompt_service_uses_category_style_and_plain_fallback_without_llm(self):
+        settings = MemoirImageSettings(
+            enabled=True,
+            max_per_chapter=2,
+            provider="liblib",
+            default_style="watercolor",
+            default_size="1024x1024",
+            poll_interval_seconds=3,
+            max_attempts=20,
+        )
+        service = MemoirImagePromptService(llm=None, settings=settings)
+
+        result = service.build_prompt(
+            chapter_title="童年的夏天",
+            chapter_category="childhood",
+            description="奶奶坐在院子里的藤椅上",
+            context_excerpt="梧桐树下很安静，夏天总有蝉鸣。",
+        )
+
+        self.assertEqual(result["style"], "watercolor")
+        self.assertEqual(result["size"], "1024x1024")
+        self.assertIn("奶奶坐在院子里的藤椅上", result["prompt"])
+        self.assertIn("childhood", result["prompt_context"])
+
+    def test_prompt_service_parses_structured_llm_response(self):
+        settings = MemoirImageSettings(
+            enabled=True,
+            max_per_chapter=2,
+            provider="liblib",
+            default_style="watercolor",
+            default_size="1024x1024",
+            poll_interval_seconds=3,
+            max_attempts=20,
+        )
+        llm = Mock()
+        llm.invoke.return_value.content = (
+            '{"prompt":"A grandmother in a quiet courtyard, summer cicadas, soft watercolor",'
+            '"style":"watercolor","size":"1024x1024"}'
+        )
+        service = MemoirImagePromptService(llm=llm, settings=settings)
+
+        result = service.build_prompt(
+            chapter_title="童年的夏天",
+            chapter_category="childhood",
+            description="奶奶坐在院子里的藤椅上",
+            context_excerpt="梧桐树下很安静，夏天总有蝉鸣。",
+        )
+
+        self.assertEqual(result["prompt"], "A grandmother in a quiet courtyard, summer cicadas, soft watercolor")
+        self.assertEqual(result["style"], "watercolor")
+        self.assertEqual(result["size"], "1024x1024")