Implement global entity search across all platform entities

[benmed00]

Problem

Users need a unified search interface to find entities across the entire platform without navigating to specific modules.

Expected Solution

Implement a global search feature that:

• Searches across all entity types (species, missions, equipment, employees, documents, publications, users, expenses, budgets, water quality, air quality, climate data)
• Provides real-time search results
• Offers intuitive UI with entity type grouping
• Supports keyboard navigation

Related

This issue is resolved by PR #75.