DO NOT MERGE: RFC: add ownership registry design documents

[martin-belanger]

RFC — posted for design review and community feedback. Not intended for merge.

One document is proposed for review, and a second is included for context:

• nvme-registry-guide.md: design guide for the NVMe controller ownership registry — a cooperative, filesystem-based mechanism that allows NVMe-oF orchestrators to declare ownership of controllers and avoid accidental disconnection of controllers managed by another orchestrator.
• nvme-orchestrator-coexistence-summary.md: companion design notes covering discovery policy coordination between nvme-discoverd and nvme-stas for environments where both daemons run simultaneously. Included for context — this is early-stage thinking, not a finished proposal.

Please use inline comments to discuss specific sections.

Related issue: #3433
Implementation PR: #3425

These documents are in Markdown format; it reads best in Typora or any Markdown-aware editor.