Create Ava environment wrapper script

Create a single wrapper script (e.g. ava-env.sh) that sets up the complete environment for Ava:

• Sources /run/secrets/ava.env for API keys
• Adds /usr/local/bin to PATH
• Loads direnv environment
• Sets CODEROOT
• Sets git user.name/email

This should be sourced at the start of pi-orchestrate.sh instead of the current scattered setup. Will make the system more maintainable and reduce manual symlink management.