USAi catalog (later): Codex / Claude Code / Copilot CLI emitters #364

Part of epic #357 (Later). Add emitters/codex.mjs (~/.codex/config.toml), emitters/claude.mjs (ANTHROPIC_BASE_URL + settings), emitters/copilot.mjs. Each: shape + no-secret tests; add a byte-exact round-trip only where a live config is already shipped. Not on prime-agent's critical path. Deps: #358, #359. Live-test: no.