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>

scripts/migrate_tools.py

@@ -1,12 +0,0 @@
-from tqdm import tqdm
-
-from letta.schemas.user import User
-from letta.services.organization_manager import OrganizationManager
-from letta.services.tool_manager import ToolManager
-
-orgs = OrganizationManager().list_organizations(cursor=None, limit=5000)
-for org in tqdm(orgs):
-    if org.name != "default":
-        fake_user = User(id="user-00000000-0000-4000-8000-000000000000", name="fake", organization_id=org.id)
-
-        ToolManager().upsert_base_tools(actor=fake_user)