Promote marketplace-status to repo root and refresh pending rows

[dstrupl]

Summary

• Rename docs/marketplace-status.md to MARKETPLACE_STATUS.md so the marketplace submission tracker sits alongside CHANGELOG.md / CONTRIBUTING.md / SECURITY.md / PRIVACY.md and is discoverable at a glance. Remove the now-empty docs/ directory.
• Re-evaluate the marketplace submission state and flip two rows from Not started to Submitted based on live GitHub data (checked 2026-04-22 UTC):
  • GitHub Copilot CLI — awesome-copilot: Submitted on 2026-04-21 via github/awesome-copilot#1461. Note added that the initial PR targeted main, the github-actions bot requested a retarget to the staged branch, and we re-pointed it the same day — so the lingering reviewDecision=CHANGES_REQUESTED is that bot review and the PR is functionally awaiting a human maintainer.
  • Cline MCP Marketplace: Submitted on 2026-04-20 via cline/mcp-marketplace#1394. No reviewer comments yet.
• Add a Last checked 2026-04-22: no reviewer response note on the Cursor Plugin Registry and Claude Code Plugins rows. Cursor has no public API for listing state, so status has to come from the in-app publisher dashboard — that's now called out in the row.
• Sync inbound links in README.md and PRD.md to the new path, update the historical entry in CHANGELOG.md, and refresh the Phase 4 deliverable bullets in PRD.md so the awesome-copilot and Cline items match the status table.

Git detected the rename at 77% similarity, so git log --follow MARKETPLACE_STATUS.md continues to traverse the original docs/ path.

Test plan

• Verify rendered Markdown on GitHub: the table in MARKETPLACE_STATUS.md, the Last refreshed: 2026-04-22 header, and all inbound links from README.md / PRD.md / CHANGELOG.md resolve.
• Confirm the two linked submissions (awesome-copilot #1461, cline/mcp-marketplace #1394) still match the stated status at review time.