feat: /diff command to view git diff (#426)

Adds `/diff` command to view git diff

codex-cli/src/components/chat/terminal-chat-input.tsx

@@ -42,6 +42,7 @@ export default function TerminalChatInput({
   openModelOverlay,
   openApprovalOverlay,
   openHelpOverlay,
+  openDiffOverlay,
   onCompact,
   interruptAgent,
   active,
@@ -64,6 +65,7 @@ export default function TerminalChatInput({
   openModelOverlay: () => void;
   openApprovalOverlay: () => void;
   openHelpOverlay: () => void;
+  openDiffOverlay: () => void;
   onCompact: () => void;
   interruptAgent: () => void;
   active: boolean;
@@ -270,6 +272,12 @@ export default function TerminalChatInput({
         return;
       }
 
+      if (inputValue === "/diff") {
+        setInput("");
+        openDiffOverlay();
+        return;
+      }
+
       if (inputValue === "/compact") {
         setInput("");
         onCompact();
@@ -494,6 +502,7 @@ export default function TerminalChatInput({
       openApprovalOverlay,
       openModelOverlay,
       openHelpOverlay,
+      openDiffOverlay,
       history,
       onCompact,
       skipNextSubmit,