fix: Add nano and vim editors to devcontainer with default editor config

[Masa1984a]

Description

This PR enhances the devcontainer editor support to fix the /memory command functionality and improve the overall developer experience.

Related Issue

Fixes #2098

Changes

• Added nano editor to fix the /memory command
• Added vim editor to provide an alternative for users who prefer it
• Set EDITOR and VISUAL environment variables to nano as the default editor
  • This ensures consistent editor behavior across various CLI tools
  • Users can still override these in their shell configuration

Why these changes?

1. nano: Required for the /memory command to work (fixes the reported issue)
2. vim: Many developers prefer vim, so including both editors provides flexibility
3. EDITOR/VISUAL: These standard environment variables ensure that:
   • Git commits open the correct editor
   • Other CLI tools that need an editor work out of the box
   • The behavior is predictable and consistent

Testing

• Built the devcontainer with the updated Dockerfile
• Verified that the /memory command now works correctly
• Confirmed both nano and vim are available
• Tested that git commit and other tools use the configured editor

Impact

This is a non-breaking change that adds two lightweight packages and sets sensible defaults while maintaining flexibility for user preferences.