VSCode Error Notifications for Critical Failures

Priority: P1

showErrorMessage is used in peripheral services (commit, Agent Manager, autocomplete). Core connection errors only go to console.error and webview postMessage.

Remaining Work

• Show showErrorMessage() when CLI binary is missing or server fails to start
• Show showWarningMessage() when SSE connection is lost (with "Retry" action)
• Avoid notification spam — throttle or deduplicate repeated errors