[docs] add a 'frequently asked questions' section to the README

[rohitsux]

We get the same three questions in design conversations:

1. "Does this run an LLM?" (no — pure code)
2. "Does any data leave my machine?" (no — local-only)
3. "What if I close my laptop mid-session?" (the daemon snapshots before suspend, resumes on wake)

Add a short FAQ section at the end of README with these three questions and crisp answers (≤2 sentences each). No new content — pull from VISION.md and ARCHITECTURE.md.