feat: Add Ruby and PHP support to sandbox

[itigges22]

Description

Add Ruby and PHP execution support to the sandbox service. These are common web development languages that would make ATLAS useful for a wider range of projects.

Requirements

• Add Ruby execution (syntax check + run)
• Add PHP execution (lint + run)
• Add language detection and aliases in sandbox/executor_server.py
• Install Ruby and PHP runtimes in sandbox Dockerfile
• Add tests for both languages
• Update docs

Context

Same pattern as existing language support in sandbox/executor_server.py. Ruby and PHP don't need a separate compilation step — just syntax checking and execution.