Task Completion Notification

Priority: P2 Issue: #6084

Remaining Work

• Show VS Code toast when session transitions to "complete" or "awaiting input" while panel is hidden
• Use showInformationMessage() for task completion, showWarningMessage() for permission requests
• Add a setting to enable/disable notifications (default: on)
• Notifications should include a "Show" button that focuses the webview panel
• Only fire when KiloProvider.panel.visible is false