fix speaker volume control and auth

- Rename USERNAME/PASSWORD to UNIFI_USERNAME/UNIFI_PASSWORD to avoid
  conflict with the Windows USERNAME system environment variable
- Set both speakerSettings.volume and speakerSettings.speakerVolume
  in the PATCH request
- Log volume before and after the change to verify it took effect

pyproject.toml

@@ -5,6 +5,6 @@ description = "Add your description here"
 readme = "README.md"
 requires-python = ">=3.14"
 dependencies = [
-    "httpx>=0.28.1",
+    "httpx[http2]>=0.28.1",
     "python-dotenv>=1.2.1",
 ]