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>

alembic/versions/08b2f8225812_adding_toolsagents_orm.py

@@ -1,58 +0,0 @@
-"""adding ToolsAgents ORM
-
-Revision ID: 08b2f8225812
-Revises: 3c683a662c82
-Create Date: 2024-12-05 16:46:51.258831
-
-"""
-
-from typing import Sequence, Union
-
-import sqlalchemy as sa
-
-from alembic import op
-from letta.settings import settings
-
-# revision identifiers, used by Alembic.
-revision: str = "08b2f8225812"
-down_revision: Union[str, None] = "3c683a662c82"
-branch_labels: Union[str, Sequence[str], None] = None
-depends_on: Union[str, Sequence[str], None] = None
-
-
-def upgrade() -> None:
-    # Skip this migration for SQLite
-    if not settings.letta_pg_uri_no_default:
-        return
-
-    # ### commands auto generated by Alembic - please adjust! ###
-    op.create_table(
-        "tools_agents",
-        sa.Column("agent_id", sa.String(), nullable=False),
-        sa.Column("tool_id", sa.String(), nullable=False),
-        sa.Column("tool_name", sa.String(), nullable=False),
-        sa.Column("id", sa.String(), nullable=False),
-        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.text("now()"), nullable=True),
-        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.text("now()"), nullable=True),
-        sa.Column("is_deleted", sa.Boolean(), server_default=sa.text("FALSE"), nullable=False),
-        sa.Column("_created_by_id", sa.String(), nullable=True),
-        sa.Column("_last_updated_by_id", sa.String(), nullable=True),
-        sa.ForeignKeyConstraint(
-            ["agent_id"],
-            ["agents.id"],
-        ),
-        sa.ForeignKeyConstraint(["tool_id"], ["tools.id"], name="fk_tool_id"),
-        sa.PrimaryKeyConstraint("agent_id", "tool_id", "tool_name", "id"),
-        sa.UniqueConstraint("agent_id", "tool_name", name="unique_tool_per_agent"),
-    )
-    # ### end Alembic commands ###
-
-
-def downgrade() -> None:
-    # Skip this migration for SQLite
-    if not settings.letta_pg_uri_no_default:
-        return
-
-    # ### commands auto generated by Alembic - please adjust! ###
-    op.drop_table("tools_agents")
-    # ### end Alembic commands ###