Document runtime /model switching and reflection layer in README and announcement copy

Summary\nUpdate the top-level README for this fork to call out runtime provider/model switching via /model, reasoning effort selection, and the experimental reflection/judge layer.\n\n## Deliverables\n- Update README.md with a concise fork-specific feature section\n- Push the change on a branch\n- Prepare announcement copy for Reddit and Hacker News\n\n## Status\nIn progress.

README update is drafted locally. Next step is commit, push, and PR creation, then I’ll prepare and publish the announcement posts.

README docs are pushed on branch and linked in PR #40: #40 . Next step is publishing the Reddit and Hacker News posts.

README docs are pushed on branch dev-rebase and linked in PR #40: #40 . Next step is publishing the Reddit and Hacker News posts.