The setting was documented but did not exist on DoclingServeConfig, so it
was silently dropped, and DoclingServeClient.from_config never forwarded
the timeout parameter it already accepted. The per-request timeout was
therefore pinned at the constructor default of 300s with no way to change
it. Add the field, forward it, and reject a non-positive value.
Also parametrize over the checked-in *.yaml.example files and validate
each through AppConfig, so an example that no longer loads fails a test
rather than a user's first run.
