[nodejs] fix local dd-trace linking regression

[watson]

Motivation

Local linking of the Node.js tracer in system-tests regressed after @dd-trace-js/package.json started to include scripts that run during npm link. Our local test workflow depended on npm link against the mounted dd-trace-js checkout, so Node.js system test images stopped picking up local tracer changes reliably.

Changes

Replace the npm link / npm link dd-trace flow with a direct symlink from /usr/app/node_modules/dd-trace to /volumes/dd-trace-js.

Apply the same fix across the shared Node.js startup scripts and the Node.js system_tests_library_version.sh scripts used by the Anthropic, Google GenAI, OpenAI, and parametric test apps.

This restores local tracer linking while avoiding link-time package scripts in the mounted dd-trace-js checkout.

Workflow

1. ⚠️ Create your PR as draft ⚠️
2. Work on you PR until the CI passes
3. Mark it as ready for review
   • Test logic is modified? -> Get a review from RFC owner.
   • Framework is modified, or non obvious usage of it -> get a review from R&P team

🚀 Once your PR is reviewed and the CI green, you can merge it!

🛟 #apm-shared-testing 🛟

Reviewer checklist

• Anything but tests/ or manifests/ is modified ? I have the approval from R&P team
• A docker base image is modified?
  • the relevant build-XXX-image label is present
• A scenario is added, removed or renamed?
  • Get a review from R&P team

[watson]

• [nodejs] fix local dd-trace linking regression #6728 👈 (View in Graphite)
• main

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[github-actions]

CODEOWNERS have been resolved as:

utils/build/docker/nodejs/anthropic_app/system_tests_library_version.sh  @DataDog/dd-trace-js @DataDog/system-tests-core
utils/build/docker/nodejs/app.sh                                        @DataDog/dd-trace-js @DataDog/system-tests-core
utils/build/docker/nodejs/google_genai_app/system_tests_library_version.sh  @DataDog/dd-trace-js @DataDog/system-tests-core
utils/build/docker/nodejs/openai_app/system_tests_library_version.sh    @DataDog/dd-trace-js @DataDog/system-tests-core
utils/build/docker/nodejs/parametric/app.sh                             @DataDog/dd-trace-js @DataDog/system-tests-core
utils/build/docker/nodejs/parametric/system_tests_library_version.sh    @DataDog/dd-trace-js @DataDog/system-tests-core