feat(ai-outfit): AI 穿搭 UI tab (§19.3) + config plumbing (§19.4)

- main_window: wrap workflow in a QStackedWidget (page 0 = print, page 1 =
  AI outfit); enable tab 2「AI 穿搭」, switch pages on tab change.
- app/widgets/ai_outfit_panel.py: three-column page per docs/11 §10 —
  left settings (Excel/output/model/prompt editor+save+insert+preview
  dialog/batch options), center (recent-results thumbnails + detail
  table), right (progress/stats/start/stop/export failures/log).
- Threading: QThread + _OutfitWorker(QObject) wraps OutfitBatchRunner;
  queued signals refresh UI, each row written back to Excel on the worker
  thread; finish summary + failure-list CSV export.
- config_service: load_ai_models()/load_outfit_prompt()/save_outfit_prompt()
  + outfit_* keys in app_config; panel persists via config_changed signal.
- tests/test_config_service.py: 8 cases for the new helpers. Full suite
  (12 files) green on Python 3.7; offscreen MainWindow smoke test passes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/services/config_service.py

@@ -14,9 +14,29 @@ DEFAULT_CONFIG = {
     "update_source": "",       # HTTP(S) manifest source (empty = no update check)
     "update_user": "",         # HTTP Basic Auth user (empty = anonymous)
     "update_pass": "",         # HTTP Basic Auth password (empty = anonymous)
+    # AI 穿搭（docs/11 §11）：上次路径与批量设置并入 app_config（密钥不在此，见 ai_models.json）
+    "outfit_excel": "",
+    "outfit_output_dir": "",
+    "outfit_model": "",            # last-selected model name
+    "outfit_concurrency": 1,
+    "outfit_request_interval": 2.0,
+    "outfit_task_cooldown": 1.0,
+    "outfit_retry_count": 2,
+    "outfit_resolution": "1K",
+    "outfit_quality": "均衡",
+    "outfit_retry_failed": False,
 }
 
 _CONFIG_FILENAME = "app_config.json"
+_AI_MODELS_FILENAME = "ai_models.json"
+_OUTFIT_PROMPT_FILENAME = "outfit_prompt.txt"
+
+# Default outfit prompt (docs/11 §7). Persisted to outfit_prompt.txt on first save.
+DEFAULT_OUTFIT_PROMPT = (
+    "为商品「{title}」（货号 {product_id}）生成人物上身实穿效果图：真人模特正面"
+    "穿着这件衣服，完整保留款式、版型、颜色与印花图案，自然光、纯色棚拍背景，"
+    "电商主图风格，不加文字与促销标签。"
+)
 
 
 def load_config():
@@ -65,3 +85,56 @@ def save_config(data):
         logger.info("Config saved to %s", config_file)
     except OSError as exc:
         logger.error("Failed to save config to %s: %s", config_file, exc)
+
+
+def load_ai_models():
+    """Load AI model configs from ai_models.json.
+
+    Returns a list of dicts (each with a ``name`` plus AiModelConfig fields).
+    Missing/corrupt file → empty list (the UI then prompts the admin to add one).
+    Keys live only in ~/.cmbot and are never committed (docs/11 §11).
+    """
+    from services.file_service import get_config_path
+    models_file = get_config_path(_AI_MODELS_FILENAME)
+    if not models_file.exists():
+        logger.info("AI models file not found: %s", models_file)
+        return []
+    try:
+        with open(str(models_file), encoding="utf-8-sig") as f:
+            data = json.load(f)
+    except (json.JSONDecodeError, ValueError, OSError) as exc:
+        logger.warning("AI models file unreadable (%s): %s", exc, models_file)
+        return []
+
+    models = data.get("models") if isinstance(data, dict) else data
+    if not isinstance(models, list):
+        logger.warning("AI models file has no model list: %s", models_file)
+        return []
+    return [m for m in models if isinstance(m, dict)]
+
+
+def load_outfit_prompt():
+    """Return the saved outfit prompt template, or the built-in default."""
+    from services.file_service import get_config_path
+    prompt_file = get_config_path(_OUTFIT_PROMPT_FILENAME)
+    if not prompt_file.exists():
+        return DEFAULT_OUTFIT_PROMPT
+    try:
+        with open(str(prompt_file), encoding="utf-8-sig") as f:
+            return f.read()
+    except OSError as exc:
+        logger.warning("Outfit prompt unreadable (%s): %s", exc, prompt_file)
+        return DEFAULT_OUTFIT_PROMPT
+
+
+def save_outfit_prompt(text):
+    """Persist the outfit prompt template (utf-8, no BOM). Does not raise."""
+    from services.file_service import get_config_path
+    prompt_file = get_config_path(_OUTFIT_PROMPT_FILENAME)
+    try:
+        prompt_file.parent.mkdir(parents=True, exist_ok=True)
+        with open(str(prompt_file), "w", encoding="utf-8") as f:
+            f.write(text)
+        logger.info("Outfit prompt saved to %s", prompt_file)
+    except OSError as exc:
+        logger.error("Failed to save outfit prompt to %s: %s", prompt_file, exc)