Log translate model/prompt, link OpenRouter key signup and leaderboard

Add opt-in usage telemetry to a private HF dataset

Hide the download file box until Get Files is clicked

Link local model name to its HF repo, unbold "local CPU model", clarify wording

Add usage explanation to top of app, covering local vs OpenRouter model choice

Switch translation backend from Gemini to OpenRouter, add test suite

Initial simplified TranslationUI: plain-text upload/download, single Buddhist translation prompt, Gemini or local CPU model