Give Khoj Long Term Memories (#1168)

# Motivation
A major component of useful AI systems is adaptation to the user
context. This is a major reason why we'd enabled syncing knowledge
bases. The next steps in this direction is to dynamically update the
evolving state of the user as conversations take place across time and
topics. This allows for more personalized conversations and to maintain
context across conversations.

# Overview
This change introduces medium and long term memories in Khoj. 
- The scope of a conversation can be thought of as short term memory. 
- Medium term memory extends to the past week.
- Long term memory extends to anytime in the past, where a search query
results in a match.

# Details
- Enable user to view and manage agent generated memories from their
settings page
- Fully integrate the memory object into all downstream usage, from
image generation, notes extraction, online search, etc.
- Scope memory per agent. The default agent has access to memories
created by other agents as well.
- Enable users and admins to enable/disable Khoj's memory system

---------

Co-authored-by: Debanjum <debanjum@gmail.com>

tests/helpers.py

@@ -4,9 +4,12 @@ import os
 from datetime import datetime
 
 import factory
+from asgiref.sync import sync_to_async
 from django.utils.timezone import make_aware
 
+from khoj.database.adapters import AgentAdapters
 from khoj.database.models import (
+    Agent,
     AiModelApi,
     ChatMessageModel,
     ChatModel,
@@ -15,8 +18,10 @@ from khoj.database.models import (
     KhojUser,
     ProcessLock,
     SearchModelConfig,
+    ServerChatSettings,
     Subscription,
     UserConversationConfig,
+    UserMemory,
 )
 from khoj.processor.conversation.utils import message_to_log
 from khoj.utils.helpers import get_absolute_path, is_none_or_empty
@@ -277,3 +282,45 @@ class ProcessLockFactory(factory.django.DjangoModelFactory):
         model = ProcessLock
 
     name = "test_lock"
+
+
+class ServerChatSettingsFactory(factory.django.DjangoModelFactory):
+    class Meta:
+        model = ServerChatSettings
+
+    memory_mode = ServerChatSettings.MemoryMode.ENABLED_DEFAULT_ON
+
+
+# Async-safe wrappers for factories and ORM operations
+async def acreate_user():
+    return await sync_to_async(UserFactory)()
+
+
+async def acreate_subscription(user):
+    return await sync_to_async(SubscriptionFactory)(user=user)
+
+
+async def acreate_chat_model():
+    return await sync_to_async(ChatModelFactory)()
+
+
+async def acreate_default_agent():
+    return await sync_to_async(AgentAdapters.create_default_agent)()
+
+
+async def acreate_agent(name, chat_model, personality):
+    return await sync_to_async(Agent.objects.create)(
+        name=name,
+        chat_model=chat_model,
+        personality=personality,
+    )
+
+
+async def acreate_test_memory(user, agent=None, raw_text="test memory"):
+    """Create a memory directly in DB without embeddings for testing."""
+    return await sync_to_async(UserMemory.objects.create)(
+        user=user,
+        agent=agent,
+        raw=raw_text,
+        embeddings=[0.1] * 384,  # Dummy embeddings
+    )