Emit Codex artifacts from compiled package output

## Problem statement Codex needs provider-visible context and skill layout that matches its conventions. The compiler should emit Codex-compatible artifacts from the generated package model without treating Claude artifacts as the default source of truth. ## Scope - Generate Codex-facing instruction content from the behavioral model and package artifacts. - Ensure generated skills and workflow summaries materialize correctly through the Codex adapter from #19. - Preserve ordered workflow intent and operational constraints in Codex-visible text. - Avoid duplicating or conflicting with the generated section maintained by materialization. ## Acceptance criteria - A generated package materializes for Codex using the existing #19 path. - `AGENTS.md`/Codex-visible context includes active package, workflow, ordered steps, constraints, and references needed to run the workflow. - Tests verify deterministic generation and no duplication of materializer-managed blocks. - The package still passes `lineage package validate` from #31. ## Dependencies - Depends on provider-neutral artifact generation. - Builds directly on the Codex materializer adapter from #19. ## Non-goals - No changes to Codex itself. - No new provider registry behavior. - No Claude-to-Codex text conversion as the primary mechanism. ## Sequencing Land after provider-neutral generation and before end-to-end behavioral validation for Codex.