🗑️ Remove AstroNvim integration files

Remove AstroNvim integration files

- Delete astronvim-integration-full.lua containing comprehensive
  AstroNvim configuration with full feature set, custom highlights,
  rainbow delimiters, and Neo-tree enhancements
- Delete astronvim-integration.lua containing minimal AstroNvim
  integration with essential plugin support and basic configuration
- Delete README-astronvim.md containing AstroNvim-specific
  installation instructions, customization examples, and
  troubleshooting guide

Removes dedicated AstroNvim integration in favor of proper
community plugin distribution.

Author: hyperb1iss