Add debug-only slash command for rollout path (#5936)

## Summary
- add a debug-only `/rollout` slash command that prints the rollout file
path or reports when none is known
- surface the new command in the slash command metadata and cover it
with unit tests

<img width="539" height="99" alt="image"
src="https://github.com/user-attachments/assets/688e1334-8a06-4576-abb8-ada33b458661"
/>

codex-rs/tui/src/chatwidget.rs

@@ -1270,7 +1270,16 @@ impl ChatWidget {
             SlashCommand::Mcp => {
                 self.add_mcp_output();
             }
-            #[cfg(debug_assertions)]
+            SlashCommand::Rollout => {
+                if let Some(path) = self.rollout_path() {
+                    self.add_info_message(
+                        format!("Current rollout path: {}", path.display()),
+                        None,
+                    );
+                } else {
+                    self.add_info_message("Rollout path is not available yet.".to_string(), None);
+                }
+            }
             SlashCommand::TestApproval => {
                 use codex_core::protocol::EventMsg;
                 use std::collections::HashMap;