Fix DeepSeek-only tests after env file moves to the repo root.

Give the routing tests a dummy key so they do not require a live .env.

periscope/src/backend/services/llm/deepseek_provider.py

@@ -362,8 +362,9 @@ class DeepSeekProvider(LLMProvider):
         api_key = settings.deepseek_api_key
         if not api_key:
             raise RuntimeError(
-                "DEEPSEEK_API_KEY is not set. Copy backend/.env.example to "
-                "backend/.env and add a key from https://platform.deepseek.com/"
+                "DEEPSEEK_API_KEY is not set. Copy "
+                "periscope/dependency/backend/.env.example to .env at the "
+                "repo root and add a key from https://platform.deepseek.com/"
             )
         self._client = AsyncOpenAI(
             api_key=api_key,

tests/test_deepseek_only.py

@@ -21,7 +21,10 @@ def restore_routing():
         "provider_validation": settings.provider_validation,
         "fallback_provider_validation": settings.fallback_provider_validation,
         "fallback_model_validation": settings.fallback_model_validation,
+        "deepseek_api_key": settings.deepseek_api_key,
     }
+    if not settings.deepseek_api_key:
+        settings.deepseek_api_key = "sk-test-not-called"
     yield
     for k, v in snap.items():
         setattr(settings, k, v)