feat(tests): add TypeScript client integration test support (#4185)

Integration tests can now validate the TypeScript SDK alongside Python
tests when running against server-mode stacks. Currently, this only adds
a _small_ number of tests. We should extend only if truly needed -- this
smoke check may be sufficient.

When `RUN_CLIENT_TS_TESTS=1` is set, the test script runs TypeScript
tests after Python tests pass. Tests are mapped via
`tests/integration/client-typescript/suites.json` which defines which
TypeScript test files correspond to each Python suite/setup combination.

The fact that we need exact "test_id"s (which are actually generated by
pytest) to be hardcoded inside the Typescript tests (so we hit the
recorded paths) is a big smell and it might become grating, but maybe
the benefit is worth it if we keep this test suite _small_ and targeted.

## Test Plan

Run with TypeScript tests enabled:
```bash
OPENAI_API_KEY=dummy RUN_CLIENT_TS_TESTS=1 \
  scripts/integration-tests.sh --stack-config server:ci-tests --suite responses --setup gpt
```

.github/workflows/integration-tests.yml

@@ -93,11 +93,27 @@ jobs:
           suite: ${{ matrix.config.suite }}
           inference-mode: 'replay'
 
+      - name: Setup Node.js for TypeScript client tests
+        if: ${{ matrix.client == 'server' }}
+        uses: actions/setup-node@39370e3970a6d050c480ffad4ff0ed4d3fdee5af # v4.1.0
+        with:
+          node-version: '20'
+          cache: 'npm'
+          cache-dependency-path: tests/integration/client-typescript/package-lock.json
+
+      - name: Setup TypeScript client
+        if: ${{ matrix.client == 'server' }}
+        id: setup-ts-client
+        uses: ./.github/actions/setup-typescript-client
+        with:
+          client-version: ${{ matrix.client-version }}
+
       - name: Run tests
         if: ${{ matrix.config.allowed_clients == null || contains(matrix.config.allowed_clients, matrix.client) }}
         uses: ./.github/actions/run-and-record-tests
         env:
           OPENAI_API_KEY: dummy
+          TS_CLIENT_PATH: ${{ steps.setup-ts-client.outputs.ts-client-path || '' }}
         with:
           stack-config: >-
             ${{ matrix.config.stack_config