feat: add toast notifications for game actions

[nitininhouse]

Summary

Adds a toast notification system to provide visual feedback for game actions.

Changes

• Created ToastManager.gd autoload for managing toast notifications
• Created toast.tscn and toast.gd for individual toast UI
• Added toast calls for key events:
  • Started (on START button)
  • Dispatching (when events are sent)
  • Route connected (on sink click)
  • Delivered (correct box type)
  • Type mismatch (wrong box type)
  • Level Complete / 🏆 All Levels Complete
  • Wrong destination (on failure)
  • Restarting (on restart)

Toast Types

• ToastManager.toast() - Default (gray)
• ToastManager.success() - Green
• ToastManager.error() - Red
• ToastManager.info() - Blue
• ToastManager.warning() - Orange

Closes #91

[knative-prow]

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This pull-request has been approved by: nitininhouse
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