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/core-lint.yml

@@ -1,63 +0,0 @@
-name: 🐍🧹 [Core] Lint and Test
-
-on:
-  pull_request:
-    branches: [ main ]
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
-  cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
-
-jobs:
-  changed-files:
-    runs-on: ubuntu-latest
-    name: changed-files
-    outputs:
-      all_changed_files: ${{ steps.changed-files.outputs.all_changed_files }}
-      any_changed: ${{ steps.changed-files.outputs.any_changed }}
-    steps:
-      - uses: actions/checkout@v4
-        with:
-          fetch-depth: 0
-      - name: Get changed files
-        id: changed-files
-        uses: tj-actions/changed-files@v44
-        with:
-          files: |
-            apps/core/**
-            .github/workflows/core-lint.yml
-  main:
-    needs: [ changed-files ]
-    if: ${{ needs.changed-files.outputs.any_changed == 'true' }}
-    runs-on: [self-hosted, medium]
-    strategy:
-      matrix:
-        python-version: ["3.12"]  # Adjust Python version matrix if needed
-
-    steps:
-    - name: Checkout
-      uses: actions/checkout@v4
-    - name: Install dependencies
-      shell: bash
-      working-directory: apps/core
-      run: uv sync --no-install-project ${{ inputs.install-args || '--extra postgres --extra external-tools --extra dev --extra cloud-tool-sandbox' }}
-    - name: Validate PR Title
-      if: github.event_name == 'pull_request'
-      uses: amannn/action-semantic-pull-request@v5
-      env:
-        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-
-    - name: Run Pyright
-      uses: jakebailey/pyright-action@v2
-      with:
-        python-version: ${{ matrix.python-version }}
-        level: "error"
-      continue-on-error: true
-
-    - name: Run Ruff Check
-      working-directory: apps/core
-      run: uv run ruff check --config pyproject.toml --diff .
-
-    - name: Run Ruff Format
-      working-directory: apps/core
-      run: uv run ruff format --config pyproject.toml --check --diff .