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/docker-entrypoint.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+set -e
+
+# Load nvm in the entrypoint environment
+export NVM_DIR="/usr/local/nvm"
+[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"
+
+# If command is bash -c, inject bashrc sourcing to make nvm available
+if [ "$1" = "bash" ] && [ "$2" = "-c" ]; then
+  shift 2
+  exec bash -c "source /etc/bash.bashrc && $*"
+else
+  exec "$@"
+fi