feat: inject Codex provider from hats

[Colafornia]

Summary

• inject each Hat's provider into Codex through startup config overrides
• treat the Hat model as an optional default while preserving user -m/--model overrides
• reject user overrides of Hat-managed provider fields
• remove the dynamic profile path and document the final behavior

Verification

• npm test: 27 passed
• npm run build: passed
• Codex 0.147.0 custom-provider launch: passed
• existing MCP configuration remained visible: passed
• Hat default model and user model override precedence: passed
• managed provider-field override rejection: passed