Switch Gemma callers to deepinfra provider

Use signed-in user's HF OAuth token for inference

Fix logout, OAuth state cleanup, HF_TOKEN diagnostic

Fix inference auth and app branding

fix: camera marker focus + black gap below content; pin Novita provider

refactor: split practice + phrases clients, share JSON repair

feat: phrases page, level picker, furigana, HF inference fix, more scenarios

feat: full redesign — dark cinematic UI, interactive dialogues, Gemma 4 31B vision