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>

.github/workflows/poetry-publish-nightly.yml

@@ -1,65 +0,0 @@
-name: uv-publish-nightly
-on:
-  schedule:
-    - cron: '35 10 * * *' # 10:35am UTC, 2:35am PST, 5:35am EST
-  release:
-    types: [published]
-  workflow_dispatch:
-
-jobs:
-  # nightly release check from https://stackoverflow.com/a/67527144
-  check-date:
-    runs-on: ubuntu-latest
-    outputs:
-      should_run: ${{ steps.should_run.outputs.should_run }}
-    steps:
-      - uses: actions/checkout@v4
-      - name: print latest_commit
-        run: echo ${{ github.sha }}
-      - id: should_run
-        continue-on-error: true
-        name: check latest commit is less than a day
-        if: ${{ github.event_name == 'schedule' }}
-        run: test -z $(git rev-list  --after="24 hours"  ${{ github.sha }}) && echo "::set-output name=should_run::false"
-
-  build-and-publish-nightly:
-    name: Build and Publish to PyPI (nightly)
-    if: github.repository == 'letta-ai/letta'  # TODO: if the repo org ever changes, this must be updated
-    runs-on: ubuntu-latest
-    needs: check-date
-    steps:
-      - name: Check out the repository
-        uses: actions/checkout@v4
-
-      - name: Set up python 3.12
-        id: setup-python
-        uses: actions/setup-python@v5
-        with:
-          python-version: 3.12
-
-      - name: Install uv
-        uses: astral-sh/setup-uv@v6
-        with:
-          enable-cache: true
-          activate-environment: true
-
-      - name: Set release version
-        run: |
-          # Extract the version number from pyproject.toml using awk
-          CURRENT_VERSION=$(awk -F '"' '/version =/ { print $2 }' pyproject.toml | head -n 1)
-          # Export the CURRENT_VERSION with the .dev and current date suffix
-          NIGHTLY_VERSION="${CURRENT_VERSION}.dev$(date +%Y%m%d%H%M%S)"
-          # Overwrite pyproject.toml with nightly config
-          sed -i "0,/version = \"${CURRENT_VERSION}\"/s//version = \"${NIGHTLY_VERSION}\"/" pyproject.toml
-          sed -i 's/name = "letta"/name = "letta-nightly"/g' pyproject.toml
-          sed -i "s/__version__ = '.*'/__version__ = '${NIGHTLY_VERSION}'/g" letta/__init__.py
-          cat pyproject.toml
-          cat letta/__init__.py
-
-      - name: Build the Python package
-        run: uv build
-
-      - name: Publish the package to PyPI
-        env:
-          UV_PUBLISH_TOKEN: ${{ secrets.PYPI_TOKEN }}
-        run: uv publish