Add Codex Maven command runner

[kevinherron]

Summary

Add Codex-facing Maven command runner instructions and remove the obsolete preflight review gate from project agent guidance.

• Add a Codex Maven runner prompt so Maven commands can be delegated to a read-only worker that captures and summarizes build output.
• Update repository instructions to make format and compile the required verification steps while leaving review gates to manual or workflow-specific processes.
• Remove the Claude preflight agent definition so future agents do not discover or invoke the stale review requirement.

Key Changes

• Verification policy: AGENTS.md no longer requires a preflight review before committing. It now keeps the Maven verification requirement and clarifies that reviews happen manually or through workflow-specific gates.
• Codex Maven delegation: The new Codex runner prompt mirrors the existing Claude runner behavior: run requested Maven commands once, capture output under /tmp/maven_*.log, analyze failures, and avoid modifying repository files.
• Agent cleanup: The unused preflight agent file is removed to keep the repository guidance aligned with the current workflow.

Testing

• Not run; this PR only changes agent and repository instruction files.