spec(overview): add prominent unofficial/AI-authored provenance callout

The book's first page previously claimed the spec was "the
authoritative definition of the wire format" derived from the
firmware. That misrepresents the project's stance. Replace the
existing "Status" block with a more honest "Status and Provenance"
block that mirrors the README disclosure:

- This is an unofficial, independent project — NOT part of the
  upstream MeshCore project, not affiliated, not endorsed.
- Primarily AI-authored (Claude / Opus 4.x) under Stephen Waits's
  direction, with human proofreading and editing.
- The upstream MeshCore C++ firmware is the source of truth;
  this spec is downstream. CHANGELOG records the upstream commit
  hash per pass.
- DongLoRa observations refine the spec but never override
  upstream.
- The corpus is a useful signal but not a substitute for
  cross-checking against upstream firmware.

Visible to anyone landing on https://swaits.github.io/meshcore-spec/
or reading the rendered overview chapter.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/00-overview.md

@@ -2,12 +2,37 @@
 
 ## Section 0: Overview
 
-### Status
+### Status and Provenance
 
-This document specifies the MeshCore mesh networking protocol as implemented in
-the [reference firmware](https://github.com/meshcore-dev/MeshCore). It is
-derived from the source code and official documentation, and serves as the
-authoritative definition of the wire format for conformance testing.
+> **This is an unofficial, independent specification.** It is **not** part of
+> the upstream [MeshCore project](https://github.com/meshcore-dev/MeshCore),
+> not affiliated with or endorsed by its maintainers, and not authored by
+> them. Read this section before relying on the spec for anything
+> load-bearing.
+
+This document was primarily written by an AI (Claude, by Anthropic — mostly
+the Opus 4.x family) under the direction of Stephen Waits, with human
+proofreading and editing on top. Substantive edits — additions, audit passes,
+errata fixes — are produced through model-driven analysis of the upstream
+MeshCore C++ source and reviewed before commit.
+
+The **upstream MeshCore C++ firmware is the source of truth** for all
+protocol behavior. This spec is downstream and derivative. Whenever the spec
+and the upstream C++ disagree, **upstream wins** — and a fix to this spec is
+filed against this repo, not against MeshCore. Each substantive change in
+[CHANGELOG.md](https://github.com/swaits/meshcore-spec/blob/main/CHANGELOG.md)
+records the upstream commit hash it was validated against.
+
+Refinements have also been driven in part by observations from building
+DongLoRa firmware and apps against live MeshCore deployments. Where DongLoRa
+behavior diverges from upstream, this spec follows upstream and treats the
+DongLoRa side as a follow-up bug, not a spec change.
+
+Conformance against the [test corpus](https://github.com/swaits/meshcore-spec/tree/main/corpus)
+is a useful signal but **not a substitute** for cross-checking against
+upstream firmware. If you find a divergence from upstream, please
+[file an issue](https://github.com/swaits/meshcore-spec/issues) — that is
+exactly the kind of report this project exists to catch.
 
 ### Scope