refactor(nvm): Move wrapper scripts to image_support_files directory

Improved code organization and maintainability:
- Created image_support_files/ directory for Docker helper scripts
- Moved bash-with-nvm and docker-entrypoint.sh to support directory
- Added comprehensive README.md documenting each script's purpose
- Updated Dockerfile to COPY from organized directory structure

Benefits:
- Cleaner repository structure
- Scripts are now version-controlled files (not echo chains)
- Easier to read, modify, and maintain
- Self-documented with in-directory README

No functional changes - all nvm functionality remains identical.

image_support_files/bash-with-nvm

@@ -0,0 +1,9 @@
+#!/bin/bash
+set -e
+
+# Load nvm before executing Dockerfile RUN commands
+export NVM_DIR="/usr/local/nvm"
+[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"
+
+# Execute the command passed to this wrapper
+eval "$@"