docs: expand Reqover Labs organization profile

[TaeHuiKKIM]

Summary

• clarify the Reqover Labs mission and the current source-built MVP status
• add direct Demo, Quickstart, Docs, Issues, contribution, and security paths
• preserve named GitHub and LinkedIn maintainer links
• narrow competition and license wording to publicly supported claims

What changed

• introduced a concise product-oriented organization hero and navigation
• summarized verified MVC/WebFlux attribution capabilities
• added a featured-project table and clear participation paths
• linked private security reporting guidance
• displayed LinkedIn links as TaeHui Kim and Sangmin Lee

Verification

• every Reqover README anchor was matched against the final main-repository README
• contribution, conduct, security, license, and third-party-notice targets were checked
• organization claims, link labels, changed-file scope, and commit authorship were audited
• final independent cross-repository review: no findings

Dependency

Merge reqover-labs/reqover#1 first so the new section anchors resolve on main.