Add persistent user preference recall across Codex CLI conversations

@VeitB I believe that’s a helpful clarification, especially the point about multiple AGENTS.md files in a project. I agree the master-project approach is a reasonable workaround for some workflows, but I think the distinction from earlier still matters: it helps with reuse of preferences, while a central preference layer would solve ownership, precedence, and lifecycle more explicitly. The nearest-AGENTS.md behavior is a good example of scoped control done well. In a monorepo, it gives the repo a way to say: “these rules apply here, not everywhere.” This maps neatly onto the repo/user/chat model: repo instructions can be local and nested, user defaults should travel across repos, and chat overrides should stay temporary. So I’d see these as complementary rather than competing mechanisms: * nested AGENTS.md for local codebase/module behavior * user defaults for cross-project working preferences * chat overrides for temporary exceptions The missing piece is making those layers visible and enforceable enough that users can trust which one is active at any moment, without a workaround blurring ownership of the context.