[vitlav]

Python 3.14 defaults to forkserver on Linux, so starting the live server fails when multiprocessing tries to pickle the nested worker function. Use the existing private fork context wherever that start method is available, preserving the application's global multiprocessing setting.

The regression test runs in a separate pytest process, selects both forkserver and spawn, and checks a real HTTP response from a local Flask route. Both cases fail with PicklingError before the change and pass afterwards. This extends the macOS repair in #161; it retains the existing fork-based server model.

Fixes #206

Validation on Python 3.14.7, Flask 3.1.3 and pytest 9.0.3: pytest -q — 35 passed, 1 existing skip; configured pre-commit hooks pass for all changed files. The existing skip and pytest configuration/deprecation warnings are unchanged.

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in docs/CHANGELOG.rst, summarizing the change and linking to the issue. (Entry added to docs/changelog.rst.)
• Run pre-commit hooks and fix any issues.
• Run pytest and make sure no tests failed.