fix: prevent notification sound on attempt_completion with queued messages

[roomote]

Summary

This PR fixes the issue where the notification sound incorrectly plays when attempt_completion is called despite having messages already queued. This was misleading users into thinking input was required when the task would actually continue automatically with the queued message.

Problem

When a user types a message during task execution, it gets queued. When the task reaches attempt_completion, the celebration sound was playing even though the queued message would be automatically processed, creating confusion about whether the task had truly paused or would continue on its own.

Solution

Added a check for messageQueue.length before playing the celebration sound. The sound now only plays when:

• The message is not partial (!isPartial)
• AND the message queue is empty (messageQueue.length === 0)

Changes

• ChatView.tsx: Added messageQueue.length === 0 condition to line 398
• Tests: Added comprehensive test suite with 4 test cases covering:
  • No sound when queue has messages
  • Sound plays when queue is empty
  • No sound with multiple queued messages
  • No sound for partial completion results

Testing

• ✅ All new tests pass
• ✅ Existing tests continue to pass
• ✅ Linting and type checking pass

Fixes #8537

---

Important

Fixes notification sound issue in ChatView.tsx by adding a condition to prevent sound when messages are queued.

• Behavior:
  • In ChatView.tsx, added messageQueue.length === 0 condition to play celebration sound only when there are no queued messages and the message is not partial.
• Tests:
  • Added ChatView.notification-sound.spec.tsx with tests for:
    • No sound when queue has messages.
    • Sound plays when queue is empty.
    • No sound with multiple queued messages.
    • No sound for partial completion results.

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[roomote]

Self-review complete: reviewing my own code like a robot auditing its reflection—optimizations detected, ego not found.

[hannesrudolph]

Tested, works.