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-unit-sqlite-test.yaml

@@ -1,60 +0,0 @@
-name: 🐍👨‍🔬 [Core] Unit Tests (SQLite)
-
-on:
-  pull_request:
-    branches:
-      - main
-  pull_request_target:
-    branches:
-      - main
-    types: [labeled]
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
-  cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
-
-jobs:
-  unit-tests:
-    # Run on pull_request OR on pull_request_target only when labeled "safe to test"
-    if: github.event_name == 'pull_request' || (github.event_name == 'pull_request_target' && contains(github.event.pull_request.labels.*.name, 'safe to test'))
-    uses: ./.github/workflows/reusable-test-workflow.yml
-    with:
-      test-type: 'sqlite'
-      use-redis: true
-      changed-files-pattern: |
-        apps/core/**
-        .github/workflows/reusable-test-workflow.yml
-        .github/workflows/core-unit-sqlite-test.yml
-      install-args: '--extra postgres --extra external-tools --extra dev --extra cloud-tool-sandbox --extra google --extra sqlite'
-      timeout-minutes: 15
-      ref: ${{ github.event.pull_request.head.sha || github.sha }}
-
-      matrix-strategy: |
-        {
-          "fail-fast": false,
-          "matrix": {
-            "include": [
-              {"test_suite": "test_client.py"},
-              {"test_suite": "test_sdk_client.py"},
-              {"test_suite": "test_server.py"},
-              {"test_suite": "test_tool_schema_parsing.py"},
-              {"test_suite": "test_tool_rule_solver.py"},
-              {"test_suite": "test_memory.py"},
-              {"test_suite": "test_utils.py"},
-              {"test_suite": "test_stream_buffer_readers.py"},
-              {"test_suite": "test_agent_serialization.py"},
-              {"test_suite": "test_optimistic_json_parser.py"},
-              {"test_suite": "test_llm_clients.py"},
-              {"test_suite": "test_letta_agent_batch.py"},
-              {"test_suite": "test_providers.py"},
-              {"test_suite": "test_sources.py"},
-              {"test_suite": "test_managers.py"},
-              {"test_suite": "sdk/"},
-              {"test_suite": "mcp_tests/", "use_experimental": true},
-              {"test_suite": "test_timezone_formatting.py"},
-              {"test_suite": "test_plugins.py"},
-              {"test_suite": "test_embeddings.py"}
-            ]
-          }
-        }
-    secrets: inherit