fix: 数据源审查小修（from_config 类型守卫/PROMPTS_KEYS 消重/契约措辞）

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

tests/test_prompt_provider.py

@@ -153,6 +153,14 @@ def test_from_config_non_string_key_raises():
              "extractor": "e", "evaluator": "v"})
 
 
+def test_from_config_non_dict_raises():
+    # 入口类型守卫: Task 6 的 PUT prompts 会把请求体直传这里——字符串/
+    # 列表进来必须是 ValueError,不能让 .get 的 AttributeError 漏成 500
+    for bad in ("system=...", ["system", "company_facts"], 42, None):
+        with pytest.raises(ValueError, match="dict"):
+            PromptProvider.from_config(bad)
+
+
 def test_from_config_equals_from_dir():
     d = JC_PROMPTS
     cfg = {name: (d / f"{name}.md").read_text(encoding="utf-8")