Production-ready: VRAM-sized batches, frontend API URL fix, repo hygiene

Replace models: new encoder + gemma-3-1b/qwen3 decoders, drop llama3

Replace dart with tick, make light mode a bit darker

Font Improvements

Dark mode added

UI improvements, background added

Fix model IDs and update decoder dropdown labels

UI improvements and HF Spaces preparation

Next.js and React implementation. UI improvements. Cloze test removed from the website.