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/test-pip-install.yml

@@ -1,23 +0,0 @@
-name: Test Package Installation
-
-on: [push, pull_request, workflow_dispatch]
-
-jobs:
-  test-install:
-    runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        python-version: ["3.11", "3.12", "3.13"]  # Adjust Python versions as needed
-
-    steps:
-    - uses: actions/checkout@v2
-    - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v2
-      with:
-        python-version: ${{ matrix.python-version }}
-
-    - name: Install package with extras
-      run: pip install '.[external-tools,postgres,dev,server,ollama]'  # Replace 'all' with the key that includes all extras
-
-    - name: Check package installation
-      run: pip list  # Or any other command to verify successful installation