feat: add nvim-tree and neotree integration

[ThomasK33]

Fixes #14

Summary

• Adds comprehensive integration with nvim-tree and neo-tree file explorers, enabling Claude to navigate and interact with project file structures
• Implements @-mention functionality for files and directories, allowing Claude to quickly reference and work with specific paths in the project

Features

• File Explorer Integration: Seamless support for both nvim-tree and neo-tree plugins
• @-mention Support: Type @filename or @directory/ to quickly reference files and folders
• Visual Commands: New visual mode commands for enhanced file interaction
• Directory Navigation: Claude can now understand and work with project directory structures

Test Coverage

• Added comprehensive unit tests for @-mention functionality (at_mention_spec.lua)
• Added directory-specific @-mention tests (directory_at_mention_spec.lua)
• Updated build system and dependencies for improved development experience

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Change-Id: I22a048a068ce66e6f6ee8c4177a2a78178ab6616