feat: implement notification service for SSE events

[markijbema]

Implements VS Code notifications for agent completion, errors, and permission requests based on user settings.

Changes

New: src/services/notification-service.ts

• NotificationService class that subscribes to SSE events via KiloConnectionService.onEvent()
• Reads notification settings from VS Code configuration (kilo-code.new.notifications.*)
• session.idle → shows info notification when agent completes (skips child sessions)
• session.error → shows warning notification on session errors (skips child sessions)
• permission.asked → shows info notification with "Go to Session" action button (5s cooldown per session)
• Caches SessionInfo from session.created/session.updated events to resolve parentID

Modified: src/services/cli-backend/types.ts

• Added session.error event type to SSEEvent union

Modified: src/services/cli-backend/connection-service.ts

• Added session.error to resolveEventSessionId() switch

Modified: src/extension.ts

• Instantiates NotificationService and adds it to dispose chain

Settings consumed (already defined in package.json)

• kilo-code.new.notifications.agent — notify on agent completion
• kilo-code.new.notifications.permissions — notify on permission requests
• kilo-code.new.notifications.errors — notify on errors

Sound settings (sounds.*) are not consumed — VS Code has no native sound API.