[codex] Attribute MCP drafts and polish README

[junseo2323]

What changed

• Attribute hosted draft_context_card writes to the authenticated Bearer token owner.
• Pass authenticated user context from the hosted MCP route into the draft handler.
• Add regression coverage for card_authors attribution.
• Redesign the GitHub README header with the live URL at the top, clearer navigation, highlights, and a shorter connection example.

Why

Hosted MCP cards were created without a card_authors row. As a result, cards, reuse outcomes, token savings, and reputation were omitted from per-user leaderboard aggregation. The README also buried the live product URL and primary onboarding path.

Impact

New cards created through the hosted MCP endpoint are credited to the API token owner, so their contributions and downstream reuse metrics appear in leaderboards and profiles. Local stdio behavior remains unchanged when no authenticated user context exists.

Validation

• npm test — 106 tests passed
• npm run typecheck
• npm run build
• npm run web:build
• git diff --check
• Fly.io production deployment health check passed