Add debug info for API key troubleshooting

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app.py

@@ -557,9 +557,11 @@ def get_client():
         os.environ.get("anthropic_api_key")
     )
     if not api_key:
+        # Debug: show env vars that contain 'key' or 'api' (names only)
+        relevant_vars = [k for k in os.environ.keys() if 'key' in k.lower() or 'api' in k.lower() or 'anthropic' in k.lower()]
         raise ValueError(
-            "Anthropic API key not found. Please add a secret in Space Settings > Repository secrets. "
-            "Try naming it: ANTHROPIC_API_KEY"
+            f"Anthropic API key not found. Available relevant env vars: {relevant_vars}. "
+            "Please add a secret named ANTHROPIC_API_KEY in Space Settings > Repository secrets."
         )
     return anthropic.Anthropic(api_key=api_key)