Add a unit test for the useTestNotification send and status handling

[Baskarayelu]

Closes #985

Summary

• Add src/hooks/__tests__/useTestNotification.test.ts with 6 focused unit tests
• Mock fetch and useToast to verify success/failure paths without real network calls
• Assert idle -> sending -> sent/error state transitions
• Cover double-send guard (second call while in-flight is a no-op)
• Cover empty channelId guard (no fetch called)
• Cover two channels tracked independently

Test plan

• pnpm test src/hooks/__tests__/useTestNotification.test.ts passes all 6 tests
• No regressions against existing test suites

🤖 Generated with Claude Code

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