docs: update sprint.md with progress summary and remaining tasks

docs: update all docs to reflect Qwen3-TTS architecture

feat: implement real voice cloning with Qwen3-TTS (sprint step 3)

feat: wire Whisper-small ASR and Qwen2.5-3B Q&A into app (sprint steps 9-10)

Update sprint.md: mark completed tasks through Day 2 morning

Update docs to reflect story_downloader pipeline and 10-story corpus

Apply design critique fixes + add README

Add interruptible chunked streaming narration + mobile considerations PRD

Rewrite PRD for 2-day hackathon + add sprint.md