feat: 完成T-301 AI生成接口

新增app/ai.py，按config/ai_models.json读取默认文本和图片模型，提供gen_title与gen_cover通用HTTP接口。

支持chat JSON与images_edits multipart、失败重试、错误脱敏、图片URL/base64解析、resolution resize和jpg_quality保存。

新增tests/test_ai.py覆盖文本重试、缺字段错误不泄露Key、封面JPEG保存；同步任务看板、API、技术栈、架构、current-state和progress，并记录Tab①真机冒烟结果。

tests/test_ai.py

@@ -0,0 +1,164 @@
+import base64
+import io
+import json
+import os
+import sys
+import unittest
+from unittest import mock
+
+sys.path.insert(0, os.path.dirname(__file__))
+
+from _helpers import TempDirMixin
+
+from app import ai, appconfig
+
+
+class _Response:
+    def __init__(self, payload):
+        self.payload = payload
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc, tb):
+        return False
+
+    def read(self, size=-1):
+        return json.dumps(self.payload).encode("utf-8")
+
+
+class AITests(TempDirMixin, unittest.TestCase):
+    def _write_models(self, path, text=None, image=None):
+        text = text or {
+            "name": "Text",
+            "category": "text",
+            "enabled": True,
+            "url": "https://example.invalid/v1/chat/completions",
+            "model": "text-model",
+            "api_key": "sk-text-secret",
+            "api_type": "chat",
+            "connect_timeout_seconds": 1,
+            "timeout_seconds": 1,
+            "extra_body": {"temperature": 0},
+        }
+        image = image or {
+            "name": "Image",
+            "category": "image",
+            "enabled": True,
+            "url": "https://example.invalid/v1/chat/completions",
+            "model": "image-model",
+            "api_key": "sk-image-secret",
+            "api_type": "auto",
+            "connect_timeout_seconds": 1,
+            "timeout_seconds": 1,
+            "extra_body": {},
+        }
+        appconfig.save_ai_models_config({"models": [text, image]}, path=path)
+
+    def _config(self):
+        cfg = appconfig.default_config()
+        cfg["ai"]["default_text_model"] = "Text"
+        cfg["ai"]["default_image_model"] = "Image"
+        cfg["ai"]["retry"] = 1
+        cfg["ai"]["resolution"] = "512"
+        cfg["ai"]["jpg_quality"] = 80
+        return cfg
+
+    def test_gen_title_uses_configured_model_and_retries(self):
+        with self.make_temp_dir() as temp_dir:
+            models_path = os.path.join(temp_dir, "ai_models.json")
+            self._write_models(models_path)
+            calls = []
+
+            def fake_urlopen(request, timeout=None):
+                calls.append((request, timeout))
+                if len(calls) == 1:
+                    raise ai.urllib.error.URLError("temporary")
+                return _Response({"choices": [{"message": {"content": " 新标题 "}}]})
+
+            with mock.patch("app.ai.urllib.request.urlopen", side_effect=fake_urlopen):
+                title = ai.gen_title(
+                    "优化标题",
+                    "旧标题",
+                    config=self._config(),
+                    models_path=models_path,
+                )
+
+            self.assertEqual("新标题", title)
+            self.assertEqual(2, len(calls))
+            body = json.loads(calls[-1][0].data.decode("utf-8"))
+            self.assertEqual("text-model", body["model"])
+            self.assertEqual(0, body["temperature"])
+            self.assertNotIn("sk-text-secret", body["messages"][1]["content"])
+
+        self.assert_removed(temp_dir)
+
+    def test_missing_model_fields_raise_clear_error_without_secret(self):
+        with self.make_temp_dir() as temp_dir:
+            models_path = os.path.join(temp_dir, "ai_models.json")
+            self._write_models(
+                models_path,
+                text={
+                    "name": "Text",
+                    "category": "text",
+                    "enabled": True,
+                    "url": "",
+                    "model": "text-model",
+                    "api_key": "sk-text-secret",
+                    "api_type": "chat",
+                    "connect_timeout_seconds": 1,
+                    "timeout_seconds": 1,
+                    "extra_body": {},
+                },
+            )
+
+            with self.assertRaises(ai.AIError) as raised:
+                ai.gen_title("prompt", "old", config=self._config(), models_path=models_path)
+
+            message = str(raised.exception)
+            self.assertIn("缺少字段: url", message)
+            self.assertNotIn("sk-text-secret", message)
+
+        self.assert_removed(temp_dir)
+
+    def test_gen_cover_saves_jpeg_with_resolution_and_quality(self):
+        try:
+            from PIL import Image
+        except ImportError:
+            self.skipTest("Pillow not installed")
+
+        with self.make_temp_dir() as temp_dir:
+            models_path = os.path.join(temp_dir, "ai_models.json")
+            self._write_models(models_path)
+            old_cover = os.path.join(temp_dir, "old.jpg")
+            output = os.path.join(temp_dir, "new.jpg")
+            Image.new("RGB", (16, 16), (20, 30, 40)).save(old_cover, "JPEG")
+            generated = io.BytesIO()
+            Image.new("RGB", (8, 8), (200, 120, 80)).save(generated, "PNG")
+            b64_image = base64.b64encode(generated.getvalue()).decode("ascii")
+
+            def fake_urlopen(request, timeout=None):
+                body = json.loads(request.data.decode("utf-8"))
+                self.assertEqual("image-model", body["model"])
+                self.assertIn("目标分辨率：512", body["messages"][0]["content"][0]["text"])
+                return _Response({"data": [{"b64_json": b64_image}]})
+
+            with mock.patch("app.ai.urllib.request.urlopen", side_effect=fake_urlopen):
+                result = ai.gen_cover(
+                    "生成封面",
+                    old_cover,
+                    output,
+                    config=self._config(),
+                    models_path=models_path,
+                )
+
+            self.assertEqual(os.path.abspath(output), result)
+            with Image.open(output) as saved:
+                self.assertEqual((512, 512), saved.size)
+                self.assertEqual("JPEG", saved.format)
+
+        self.assert_removed(temp_dir)
+
+
+if __name__ == "__main__":
+    unittest.main()