refactor: Cut dead code paths

[CSRessel]

Summary

• remove the legacy debug-only /rollout and /test-approval slash commands from the TUI command surface and their dead handlers/tests
• trim compatibility-only login_status and auth_manager fields from the Nori onboarding args so the Nori path only carries live data
• delete the orphaned top-level update modules and stale snapshot, and refresh codex-rs/tui/docs.md so it documents the Nori update path that actually ships in nori

Why

This PR is a dead-code cleanup pass focused on the ACP-backed Nori CLI. It removes compatibility baggage and uncompiled upstream leftovers from nori-tui, which keeps the branch net-negative and reduces accidental complexity in the code that matters for the nori binary.

Validation

• RUSTC_WRAPPER= cargo test -p nori-tui --manifest-path codex-rs/Cargo.toml
• RUSTC_WRAPPER= cargo build --bin nori --manifest-path codex-rs/Cargo.toml
• RUSTC_WRAPPER= cargo test -p tui-pty-e2e --manifest-path codex-rs/Cargo.toml
• RUSTC_WRAPPER= just fix -p nori-tui
• just fmt
• launched ./target/debug/nori --agent elizacp --skip-trust-directory in an isolated tmux session, submitted hello, observed an ElizACP reply, and verified the prompt returned