crimx/ext-saladict ? reverse-engineered prompt

Build me a browser extension called Saladict that helps me translate words and phrases right inside the page.

I want it to work in Chrome and Firefox, with a clean, fast popup when I select text or hover over it. It should support multiple lookup modes, page translation, a place to save new words, and searching selected text in PDFs too. Make it feel smooth and customizable, not clunky, and include a nice dictionary panel that can show results from more than one source.

Please set it up so I can build it from source and run it locally, and if you need current setup details from the web, look them up. I also want the extension to feel polished enough to ship, with the core screens, settings, and basic onboarding handled.