refactor: update shell scripts for AI-Trader-Server rebrand

Update all shell scripts to use the new AI-Trader-Server naming throughout.

Changes:
- main.sh: Update comments and echo statements
- entrypoint.sh: Update startup message
- scripts/validate_docker_build.sh: Update title, container name references,
  and docker image tag from ai-trader-test to ai-trader-server-test
- scripts/test_api_endpoints.sh: Update title and docker-compose command

Part of Phase 4: Internal Configuration & Metadata (Task 19)

entrypoint.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 set -e  # Exit on any error
 
-echo "🚀 Starting AI-Trader API Server..."
+echo "🚀 Starting AI-Trader-Server API..."
 
 # Validate required environment variables
 echo "🔍 Validating environment variables..."