docs: reframe Every Code product identity

[cbusillo]

Summary

• Reframe README, AGENTS, repo metadata, and maintainer import docs around Every Code as the product identity
• Preserve upstream Codex / just-every/code language as provenance and import policy rather than lead identity
• Update owned runtime prompt identity surfaces to introduce Code as the Every Code CLI agent while leaving Codex model/wire slugs intact

Prompt-file note

Two read-only agents audited the diff. One flagged Codex-compatible model prompt headers as a possible overreach; after checking runtime injection, I kept the Every Code header because it is the product identity text we send from our runtime, while Codex model names/slugs remain unchanged for compatibility.

Validation

• jq empty .github/github.json
• git diff --check
• ./build-fast.sh
• Changed-file JetBrains inspection was attempted; it reported 0 problems but timed out before a stable clean capture.

Refs #86
Parent #85