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/warn_poetry_updates.yml

@@ -1,63 +0,0 @@
-name: Check uv Dependencies Changes
-
-on:
-  pull_request:
-    paths:
-      - 'uv.lock'
-      - 'pyproject.toml'
-
-jobs:
-  check-uv-changes:
-    runs-on: ubuntu-latest
-    permissions:
-      pull-requests: write
-
-    steps:
-      - uses: actions/checkout@v4
-        with:
-          fetch-depth: 0
-
-      - name: Check for uv.lock changes
-        id: check-uv-lock
-        run: |
-          if git diff --name-only ${{ github.event.pull_request.base.sha }} ${{ github.event.pull_request.head.sha }} | grep -q "uv.lock"; then
-            echo "uv_lock_changed=true" >> $GITHUB_OUTPUT
-          else
-            echo "uv_lock_changed=false" >> $GITHUB_OUTPUT
-          fi
-
-      - name: Check for pyproject.toml changes
-        id: check-pyproject
-        run: |
-          if git diff --name-only ${{ github.event.pull_request.base.sha }} ${{ github.event.pull_request.head.sha }} | grep -q "pyproject.toml"; then
-            echo "pyproject_changed=true" >> $GITHUB_OUTPUT
-          else
-            echo "pyproject_changed=false" >> $GITHUB_OUTPUT
-          fi
-
-      - name: Create PR comment
-        if: steps.check-uv-lock.outputs.uv_lock_changed == 'true' || steps.check-pyproject.outputs.pyproject_changed == 'true'
-        uses: actions/github-script@v7
-        with:
-          script: |
-            const uvLockChanged = ${{ steps.check-uv-lock.outputs.uv_lock_changed }};
-            const pyprojectChanged = ${{ steps.check-pyproject.outputs.pyproject_changed }};
-
-            let message = '📦 Dependencies Alert:\n\n';
-
-            if (uvLockChanged && pyprojectChanged) {
-              message += '- Both `uv.lock` and `pyproject.toml` have been modified\n';
-            } else if (uvLockChanged) {
-              message += '- `uv.lock` has been modified\n';
-            } else if (pyprojectChanged) {
-              message += '- `pyproject.toml` has been modified\n';
-            }
-
-            message += '\nPlease review these changes carefully to ensure they are intended (cc @sarahwooders @cpacker).';
-
-            github.rest.issues.createComment({
-              issue_number: context.issue.number,
-              owner: context.repo.owner,
-              repo: context.repo.repo,
-              body: message
-            });