Nexus runtime: audio, package progress and cloud saves

• Implement communication audio endpoint queries and change notifications requested by games such as Deep Rock Galactic.
• Correct installed-package byte totals and unknown-size reporting used by game progress queries.
• Preserve local saves when cloud transfers fail or conflict with pending local changes, and reject incomplete cloud metadata.
• Keep final save-upload notifications through session shutdown and report cloud-upload failures correctly.

Update the launcher to 0.3.11 and the backend to 0.2.11 in Settings. These fixes address specific runtime issues; they do not mean that all reported game-compatibility problems are resolved.