Remove env fallback for API key - UI input only

.env.example

@@ -1,3 +1,3 @@
 # STACKNET Configuration
 STACKNET_NETWORK_URL=https://geoffnet.magma-rpc.com
-STACKNET_SERVICE_KEY=
+# Note: API key is entered via the UI Settings field, not from environment

src/api/client.py

@@ -58,7 +58,7 @@ class StackNetClient:
         timeout: float = 300.0
     ):
         self.base_url = base_url or config.stacknet_url
-        self.api_key = api_key or config.stacknet_api_key
+        self.api_key = api_key  # Must be provided from UI, no env fallback
         self.timeout = timeout
         self._temp_dir = tempfile.mkdtemp(prefix="stacknet_")
 

src/config.py

@@ -18,7 +18,7 @@ class Config:
 
     # StackNet API
     stacknet_url: str = os.getenv("STACKNET_NETWORK_URL", "https://geoffnet.magma-rpc.com")
-    stacknet_api_key: str = os.getenv("STACKNET_SERVICE_KEY", "")
+    # Note: API key is provided via UI only, not from environment
 
     # Endpoints
     @property