feat(webui): add new chat keyboard shortcut

Add Cmd/Ctrl+Shift+O shortcut to start a new chat, matching the
convention used by ChatGPT, Claude.ai, and Gemini.

Addresses #4178

Signed-off-by: axelray-dev <110029405+axelray-dev@users.noreply.github.com>

webui/src/App.tsx

@@ -1007,6 +1007,13 @@ function Shell({
   useEffect(() => {
     const handleKeyDown = (event: globalThis.KeyboardEvent) => {
       if (event.defaultPrevented) return;
+      const commandShiftO =
+        (event.metaKey || event.ctrlKey) && event.shiftKey && !event.altKey;
+      if (commandShiftO && event.key.toLowerCase() === "o") {
+        event.preventDefault();
+        onNewChat();
+        return;
+      }
       const plainCommandK =
         (event.metaKey || event.ctrlKey) && !event.altKey && !event.shiftKey;
       if (!plainCommandK) return;
@@ -1017,7 +1024,7 @@ function Shell({
 
     window.addEventListener("keydown", handleKeyDown);
     return () => window.removeEventListener("keydown", handleKeyDown);
-  }, [onOpenSessionSearch]);
+  }, [onNewChat, onOpenSessionSearch]);
 
   const onSelectSearchResult = useCallback(
     (key: string) => {

webui/src/tests/app-layout.test.tsx

@@ -1354,6 +1354,26 @@ describe("App layout", () => {
     expect(createChatSpy).not.toHaveBeenCalled();
   });
 
+  it("starts a new chat from the keyboard shortcut", async () => {
+    mockSessions = [
+      {
+        key: "websocket:chat-a",
+        channel: "websocket",
+        chatId: "chat-a",
+        createdAt: "2026-04-16T10:00:00Z",
+        updatedAt: "2026-04-16T10:00:00Z",
+        preview: "Existing chat",
+      },
+    ];
+
+    render(<App />);
+
+    await waitFor(() => expect(connectSpy).toHaveBeenCalled());
+    fireEvent.keyDown(window, { key: "O", shiftKey: true, metaKey: true });
+
+    expect(window.location.hash).toBe("#/new");
+  });
+
   it("keeps large sidebars light while search still covers every chat", async () => {
     mockSessions = Array.from({ length: 170 }, (_, index) => {
       const chatId = `chat-${index}`;