feat(db & e2e): Enhance DB Schemas/Controllers and Improve E2E Tests (#966)

* feat: add global teardown to remove test data and add registration/log-out to auth flow

* refactor(models/Conversation): index user field and add JSDoc to deleteConvos

* refactor: add user index to message schema and ensure user is saved to each Message

* refactor: add user to each saveMessage call

* fix: handle case where title is null in zod schema

* feat(e2e): ensure messages are deleted on cleanUp

* fix: set last convo for all endpoints on conversation update

* fix: enable registration for CI env

api/models/Message.js

@@ -7,6 +7,7 @@ module.exports = {
   Message,
 
   async saveMessage({
+    user,
     messageId,
     newMessageId,
     conversationId,
@@ -33,6 +34,7 @@ module.exports = {
       await Message.findOneAndUpdate(
         { messageId },
         {
+          user,
           messageId: newMessageId || messageId,
           conversationId,
           parentMessageId,