Semantic roots in v2 API; evaluator metadata propagated to…

feat(ui): show media size in preview by @hassiebp in https://github.com/langfuse/langfuse/pull/15682
feat(metrics): expose semantic roots in v2 API by @sumerman in https://github.com/langfuse/langfuse/pull/15633
feat(preview): sign in automatically as the demo user on previews by @nmtrang29 in https://github.com/langfuse/langfuse/pull/15579

fix(in-app-agent): keep drafts editable while running by @LysanderKie in https://github.com/langfuse/langfuse/pull/15666
fix: reject bad methods on api/public/signup route by @Steffen911 in https://github.com/langfuse/langfuse/pull/15670
fix(evals): propagate evaluator metadata to generation spans by @wochinge in https://github.com/langfuse/langfuse/pull/15665
fix(web): hide migration activity indicator for dormant env-gated migrations by @Steffen911 in https://github.com/langfuse/langfuse/pull/15676
fix(evals): prevent recursion through OpenRouter Broadcast by @hassiebp in https://github.com/langfuse/langfuse/pull/15669
fix(v4): detect legacy dataset run GET APIs by @marliessophie in https://github.com/langfuse/langfuse/pull/15677
fix(widgets): derive minVersion from widget shape by @sumerman in https://github.com/langfuse/langfuse/pull/15655
fix(dashboards): preserve legacy traces v4 compatibility by @sumerman in https://github.com/langfuse/langfuse/pull/15687

chore(pricing): correct gpt-5.6-terra and gpt-5.6-luna price cuts by @langfuse-bot in https://github.com/langfuse/langfuse/pull/15659
chore: move entity change event queued log to debug by @Steffen911 in https://github.com/langfuse/langfuse/pull/15705
chore(deps): bump brace-expansion to 1.1.18, 2.1.4, and 5.0.9 by @bezbac in https://github.com/langfuse/langfuse/pull/15708

Full Changelog: https://github.com/langfuse/langfuse/compare/v4.2.0...v4.3.0

Semantic roots in v2 API; evaluator metadata propagated to spans