v0.2.8 — Fix follow_traces not firing

Bug Fix

follow_traces enrichment never fired when the server was started with --service-name because the handler and provider disagreed on the effective service name.

The browser sends service= (empty) on normal polls. The handler normalized this to None and passed it to both poll_new_spans and the follow_traces condition. The provider had its own fallback (config.service_name), so it filtered correctly — but the handler's if service_name check was always False, skipping trace-follow entirely.

Fix

• server.py: Resolve effective_service from request param > server config before both poll_new_spans and the follow_traces check
• signoz_provider.py: Remove provider-level config.service_name fallback — caller resolves defaults
• Tests updated to match new single-resolution behavior