fix(postmessage): improve tab identification logic in _onLoad event

[hymccord]

Fixes: #68

[Copilot]

Pull Request Overview

This PR fixes tab identification logic in the _onLoad event handler by replacing incorrect array indexing with proper tab lookup by ID. The change ensures that when a child tab sends a LOADED message with its UUID, the parent correctly identifies and updates the specific tab rather than assuming it's the last tab in the array.

• Replaces last-tab assumption with ID-based tab lookup using arrayUtils.searchByKeyName
• Adds null check to prevent errors when the specified tab ID is not found
• Maintains existing tab property updates only when the target tab is successfully located

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