🧪 feat: Experimental: Enable Switching Endpoints Mid-Conversation (#1483)

* fix: load all existing conversation settings on refresh

* refactor(buildDefaultConvo): use `lastConversationSetup.endpointType` before `conversation.endpointType`

* refactor(TMessage/messageSchema): add `endpoint` field to messages to differentiate generation origin

* feat(useNewConvo): `keepLatestMessage` param to prevent reseting the `latestMessage` mid-conversation

* style(Settings): adjust height styling to allow more space in dialog for additional settings

* feat: Modular Chat: experimental setting to Enable switching Endpoints mid-conversation

* fix(ChatRoute): fix potential parsing issue with tPresetSchema

client/src/components/Nav/SettingsTabs/General/ModularChat.tsx

@@ -0,0 +1,35 @@
+import { useRecoilState } from 'recoil';
+import { Switch } from '~/components/ui';
+import { useLocalize } from '~/hooks';
+import store from '~/store';
+
+export default function ModularChatSwitch({
+  onCheckedChange,
+}: {
+  onCheckedChange?: (value: boolean) => void;
+}) {
+  const [modularChat, setModularChat] = useRecoilState<boolean>(store.modularChat);
+  const localize = useLocalize();
+
+  const handleCheckedChange = (value: boolean) => {
+    setModularChat(value);
+    if (onCheckedChange) {
+      onCheckedChange(value);
+    }
+  };
+
+  return (
+    <div className="flex items-center justify-between">
+      <div>
+        {`[${localize('com_ui_experimental')}]`} {localize('com_nav_modular_chat')}{' '}
+      </div>
+      <Switch
+        id="modularChat"
+        checked={modularChat}
+        onCheckedChange={handleCheckedChange}
+        className="ml-4 mt-2"
+        data-testid="modularChat"
+      />
+    </div>
+  );
+}