Feature: Add a search/filter bar for the file tree

[MinhKhoixyz]

💡 The Problem

When loading a large project with hundreds of files, it becomes difficult to manually scroll and find specific files to include/exclude in the context export.

✨ Proposed Solution

Add a simple search/filter input bar above the ASCII tree. As the user types, the tree should dynamically filter and only show files/folders matching the search query.

🛠️ Tasks

• Add a search input UI component.
• Implement filtering logic for the file tree state.
• Ensure parent directories remain visible if a child file matches the query.