Support changing reasoning effort (#2435)

https://github.com/user-attachments/assets/50198ee8-5915-47a3-bb71-69af65add1ef

Building up on #2431 #2428

codex-rs/tui/src/slash_command.rs

@@ -12,6 +12,7 @@ use strum_macros::IntoStaticStr;
 pub enum SlashCommand {
     // DO NOT ALPHA-SORT! Enum order is presentation order in the popup, so
     // more frequently used commands should be listed first.
+    Model,
     New,
     Init,
     Compact,
@@ -36,6 +37,7 @@ impl SlashCommand {
             SlashCommand::Diff => "show git diff (including untracked files)",
             SlashCommand::Mention => "mention a file",
             SlashCommand::Status => "show current session configuration and token usage",
+            SlashCommand::Model => "choose a model preset (model + reasoning effort)",
             SlashCommand::Mcp => "list configured MCP tools",
             SlashCommand::Logout => "log out of Codex",
             #[cfg(debug_assertions)]