Reflection follow-up: rewrite missing substrate file auth.json (codex)

Missing path: ~/.codex/auth.json Referenced in: FLEET-TOOLS.md line 440 and CODING-AGENT-FALLBACKS.md lines 18 and 88. Presumed contents: Codex (OpenAI coding CLI) authentication credentials. FLEET-TOOLS.md states codex auth is stored here. Docs claim: "Codex: logged in via ~/.codex/auth.json (uses OPENAI_API_KEY)". This is likely the authentication state file created by running `codex login` or `codex auth`. Fix: run `codex login` with the OPENAI_API_KEY from the gateway env, or manually write the auth.json with the API key. Verify codex binary is installed: `which codex`.