Move CodexAuth and AuthManager to the core crate (#3074)

Fix a long standing layering issue.

codex-rs/tui/src/app.rs

@@ -7,10 +7,10 @@ use crate::pager_overlay::Overlay;
 use crate::tui;
 use crate::tui::TuiEvent;
 use codex_ansi_escape::ansi_escape_line;
+use codex_core::AuthManager;
 use codex_core::ConversationManager;
 use codex_core::config::Config;
 use codex_core::protocol::TokenUsage;
-use codex_login::AuthManager;
 use color_eyre::eyre::Result;
 use crossterm::event::KeyCode;
 use crossterm::event::KeyEvent;