[Herklos]

Summary

Adds a GitHub Actions workflow that runs the chat example backend's pytest suite (examples/app/backend/tests).

• Triggers on pull_request and on pushes to master.
• Runs uv run --python 3.12 pytest tests/ -v from examples/app/backend. The dev test dependencies come from the project's dependency group, which uv run includes by default.
• Job fails when any test fails, and has a 10 minute timeout. The local suite takes about 20 seconds.
• The existing PyPI, npm, and docs deploy workflows are unchanged.
• Adds a CHANGELOG entry under the current version.

Current status of CI

On master the job is red. Four tests in examples/app/backend/tests/test_edge.py are stale and fail against the current server behavior. This is expected, and the job is working as intended: it shows the failures.

This PR should merge after #80, which updates those four tests. With #80's test file applied locally, the suite passes (121 tests).

Testing

• Local run on the master base: 117 passed, 4 failed (the stale test_edge.py tests above).
• Local run with Align example backend edge tests with current server behavior #80's test_edge.py applied: 121 passed.
• The workflow YAML parses cleanly.