Initial implementation of /init (#1822)

Basic /init command that appends an instruction to create AGENTS.md to
the conversation history.

codex-rs/tui/src/chatwidget.rs

@@ -575,6 +575,16 @@ impl ChatWidget<'_> {
         }
     }
 
+    /// Programmatically submit a user text message as if typed in the
+    /// composer. The text will be added to conversation history and sent to
+    /// the agent.
+    pub(crate) fn submit_text_message(&mut self, text: String) {
+        if text.is_empty() {
+            return;
+        }
+        self.submit_user_message(text.into());
+    }
+
     pub(crate) fn token_usage(&self) -> &TokenUsage {
         &self.token_usage
     }