Refine global Codex instructions

[sreejithraman]

Summary

• add shared global work and verification preferences
• move delegation and review routing into skill descriptions
• archive the worktree preflight as optional SreeStack files
• move the preflight script and tests into codex/scripts
• document optional setup and review expectations

Why

Keep always-loaded global instructions focused while letting skill descriptions route specialized workflows. Preserve the worktree preflight for later use without enabling it in the live Codex setup.

User effect

The live global instructions match SreeStack. The old workspace hook and active rule are removed. The preflight remains available as an explicit opt-in.

Verification

• node --test codex/scripts/worktree-start.test.mjs (23 passed)
• python3 scripts/check_skills.py
• skill validation for orchestration and review-fix-loop
• git diff --check
• shared/live global instruction comparison
• optional and active rule matching checks
• clean independent review by two native reviewers and Gemini