Vaadin 25.1: Free Copilot and production-ready Signals

Vaadin 25.1 is the first feature release in the 25.x line. Key highlights include: Vaadin Copilot is now free for all users with a redesigned toolbar-based interface; Signals move to production-ready status, offering a reactive state management model in plain Java with component bindings, local/shared/computed state support; and browserless UI testing (previously commercial TestBench) is now free and open source under Apache 2.0. The release also adds new components including Slider, RangeSlider, and Badge (in Preview), modular Upload architecture, AI integration APIs via AIOrchestrator with Spring AI and LangChain4j support, Map drawing improvements, Grid scroll-to-column API, and Dialog viewport constraints. Additionally, SwingBridge is introduced as a separate tool to run Java Swing apps in the browser.