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>

init.sql

@@ -1,36 +0,0 @@
--- Title: Init Letta Database
-
--- Fetch the docker secrets, if they are available.
--- Otherwise fall back to environment variables, or hardwired 'letta'
-\set db_user `([ -r /var/run/secrets/letta-user ] && cat /var/run/secrets/letta-user) || echo "${POSTGRES_USER:-letta}"`
-\set db_password `([ -r /var/run/secrets/letta-password ] && cat /var/run/secrets/letta-password) || echo "${POSTGRES_PASSWORD:-letta}"`
-\set db_name `([ -r /var/run/secrets/letta-db ] && cat /var/run/secrets/letta-db) || echo "${POSTGRES_DB:-letta}"`
-
--- CREATE USER :"db_user"
---     WITH PASSWORD :'db_password'
---     NOCREATEDB
---     NOCREATEROLE
---     ;
---
--- CREATE DATABASE :"db_name"
---     WITH
---     OWNER = :"db_user"
---     ENCODING = 'UTF8'
---     LC_COLLATE = 'en_US.utf8'
---     LC_CTYPE = 'en_US.utf8'
---     LOCALE_PROVIDER = 'libc'
---     TABLESPACE = pg_default
---     CONNECTION LIMIT = -1;
-
--- Set up our schema and extensions in our new database.
-\c :"db_name"
-
-CREATE SCHEMA :"db_name"
-    AUTHORIZATION :"db_user";
-
-ALTER DATABASE :"db_name"
-    SET search_path TO :"db_name";
-
-CREATE EXTENSION IF NOT EXISTS vector WITH SCHEMA :"db_name";
-
-DROP SCHEMA IF EXISTS public CASCADE;