NIP-34: Multi-maintainer semantics + NIP-32 guidance for assignees/reviewers

[chebizarro]

Summary

This PR updates NIP-34 in two focused ways:

1. Multi-maintainer repositories:
   Clarifies that each maintainer publishes their own 30617 (repository announcement) and 30618 (state) events. Specifies that clients should:

   • De-duplicate by (d, euc) (same repo id + earliest unique commit).
   • Surface per-maintainer metadata when fields conflict (no single canonical source is mandated by the spec).
   • Treat multiple maintainers as parallel, valid views of the same repo identity.

2. NIP-32 integration (labels) for workflow metadata:
   Adds concise guidance for using NIP-32 labels (kind:1985) to model:

   • Assignees on issues (kind:1621)
   • Reviewers on patches (kind:1617)
     without introducing new kinds. Includes example tags and recommended label namespaces.

Motivation

• Multi-maintainer repos are already common; clients needed a minimal, interoperable rule-set to reconcile multiple 30617/30618 streams.
• Assigning people and designating reviewers is widely requested; NIP-32 labels provide a simple, backwards-compatible mechanism.

What changed (spec-only)

• Added a short subsection defining per-maintainer 30617/30618 expectations and client behavior for conflicts.
• Added a short subsection showing how to apply NIP-32 labels for assignees and reviewers (example tag patterns and suggested label namespacing).

Backwards compatibility

• No breaking changes. These are clarifications and optional usage guidance aligning with existing practices.