GPT-5.6 usage aliases added; legacy trace widgets now use v2

What's Changed

Fixes

• fix(pricing): add GPT-5.6 usage aliases by @hassiebp in https://github.com/langfuse/langfuse/pull/15712
• fix(dashboards): route legacy trace widgets through v2 by @sumerman in https://github.com/langfuse/langfuse/pull/15685
• fix(ci): add required cache-key to Blacksmith Docker builder setup by @LysanderKie in https://github.com/langfuse/langfuse/pull/15720

Chores

• chore(pricing): validate usage-key coverage by @hassiebp in https://github.com/langfuse/langfuse/pull/15713
• chore(web): Enable no-style-props rule globally by @bezbac in https://github.com/langfuse/langfuse/pull/15711

Full Changelog: https://github.com/langfuse/langfuse/compare/v4.3.0...v4.3.1