fix: empty track_uris guard, None duration handling, README env block

README.md

@@ -52,13 +52,20 @@ Add the MCP server to your Claude Code configuration by editing `~/.claude/setti
   "mcpServers": {
     "spotify": {
       "command": "/absolute/path/to/mcp-spotify/.venv/bin/python",
-      "args": ["/absolute/path/to/mcp-spotify/server.py"]
+      "args": ["/absolute/path/to/mcp-spotify/server.py"],
+      "env": {
+        "SPOTIPY_CLIENT_ID": "your_client_id_here",
+        "SPOTIPY_CLIENT_SECRET": "your_client_secret_here",
+        "SPOTIPY_REDIRECT_URI": "http://localhost:8888/callback"
+      }
     }
   }
 }
 ````
 
-**Note:** Replace `/absolute/path/to/mcp-spotify` with the actual path to your project. To find it, run `pwd` in the project directory:
+**Note:** Replace the path and fill in the env values with your actual Spotify app credentials. The `env` block is required because Claude Code launches the server as a subprocess from a different working directory where `load_dotenv()` may not find your `.env` file.
+
+Replace `/absolute/path/to/mcp-spotify` with the actual path to your project. To find it, run `pwd` in the project directory:
 
 ```bash
 cd /path/to/mcp-spotify