kde/kdenlive — reverse-engineered prompt

Build me a polished free desktop video editor that feels approachable for beginners but still powerful enough for bigger projects. I want people to be able to import video, audio, and images, arrange them on a timeline, trim and split clips, add transitions, apply video and audio effects, preview the result, and export the finished video in common formats. It should support saving and reopening projects, show thumbnails and waveforms where helpful, and generally feel fast and stable for real editing work.

Please make it feel like a real end user app, not just a demo. A clean interface, solid playback, sensible defaults, and good error handling matter a lot. Since this is meant to be open source and community friendly, keep it easy to build, easy to translate, and well documented for contributors.

Use the project docs as the source of truth for setup and architecture, and look up current docs online if you need to. I want something close to a usable Kdenlive style editor by the end.