Test: Implement E2E: Global Unified Search and Debounce Logic

[spiffamani]

Summary

• Adds E2E coverage for global unified search debounce: rapid typing does not hit the API until the user pauses, then a single request is made with the final query.
• Implements the search stack those tests exercise (GlobalSearch, useGlobalSearch, globalSearchService) across deliveries, drivers, and transactions.
• Covers the happy path, empty/whitespace input, API errors, result selection, and clearing a pending debounce.

Closes #483

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