* 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
