Restructure README header and move Space config to CONTRIBUTING

[rajdeepchatale]

Summary

• Removes the table at the top of the README. GitHub was rendering the Hugging Face YAML front matter as a table above the title. The config now lives in CONTRIBUTING.md under "Deploying to Hugging Face Spaces", with instructions for applying it. openenv push adds a header automatically when deploying.
• Reorders the README. It now opens with a centered title, tagline, badges and quick links (Quickstart · Example · Tasks · Reward · Live Space), then Overview → Highlights → How it works → Example episode → Quickstart, with the reference sections after.
• Adds an example episode taken from the environment itself. The first attempt misses a filter and gets 0.82 with a MISSING_ROWS diagnostic; the corrected query scores 0.97 and ends the episode.

Verification

• Rendered through GitHub's Markdown API: <h1> comes first, no table precedes it, and all 16 sections appear in order.
• openenv validate . still passes; no code changes.

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