chore: officially migrate to submodule (#4502)

* remove apps/core and apps/fern

* fix precommit

* add submodule updates in workflows

* submodule

* remove core tests

* update core revision

* Add submodules: true to all GitHub workflows

- Ensure all workflows can access git submodules
- Add submodules support to deployment, test, and CI workflows
- Fix YAML syntax issues in workflow files

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* remove core-lint

* upgrade core with latest main of oss

---------

Co-authored-by: Claude <noreply@anthropic.com>

examples/docs/rest_client.py

@@ -1,58 +0,0 @@
-from letta_client import CreateBlock, Letta, MessageCreate
-
-"""
-Make sure you run the Letta server before running this example.
-```
-letta server
-```
-"""
-
-
-def main():
-    # Connect to the server as a user
-    client = Letta(base_url="http://localhost:8283")
-
-    # list available configs on the server
-    llm_configs = client.models.list_llms()
-    print(f"Available LLM configs: {llm_configs}")
-    embedding_configs = client.models.list_embedding_models()
-    print(f"Available embedding configs: {embedding_configs}")
-
-    # Create an agent
-    agent_state = client.agents.create(
-        name="my_agent",
-        memory_blocks=[
-            CreateBlock(
-                label="human",
-                value="My name is Sarah",
-            ),
-            CreateBlock(
-                label="persona",
-                value="I am a friendly AI",
-            ),
-        ],
-        model=llm_configs[0].handle,
-        embedding=embedding_configs[0].handle,
-    )
-    print(f"Created agent: {agent_state.name} with ID {str(agent_state.id)}")
-
-    # Send a message to the agent
-    print(f"Created agent: {agent_state.name} with ID {str(agent_state.id)}")
-    response = client.agents.messages.create(
-        agent_id=agent_state.id, 
-        messages=[
-            MessageCreate(
-                role="user",
-                content="Whats my name?",
-            )
-        ],
-    )
-    print(f"Received response:", response.messages)
-
-    # Delete agent
-    client.agents.delete(agent_id=agent_state.id)
-    print(f"Deleted agent: {agent_state.name} with ID {str(agent_state.id)}")
-
-
-if __name__ == "__main__":
-    main()