Add comprehensive spec audit results and pyMC_core issue reports

- CHANGELOG.md: Full audit findings organized by severity
- PYMC_CORE_ISSUES.md: 7 evidence-based bug reports for pyMC_core
  (wrong constants, broken path_len decoding, wrong TRACE hash,
  wrong SNR calculation)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Add comprehensive spec audit results and pyMC_core issue reports

- CHANGELOG.md: Full audit findings organized by severity
- PYMC_CORE_ISSUES.md: 7 evidence-based bug reports for pyMC_core
  (wrong constants, broken path_len decoding, wrong TRACE hash,
  wrong SNR calculation)
- Remove ERRATA.md: contents already covered by audit findings

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

README.md

@@ -0,0 +1,70 @@
+# MeshCore Spec
+
+A comprehensive specification and conformance test suite for the
+[MeshCore](https://github.com/meshcore-dev/MeshCore) mesh networking protocol.
+
+MeshCore Spec aims to be the authoritative, machine-readable definition of the
+MeshCore wire format — much like [RubySpec](https://github.com/ruby/spec) became
+the definitive specification of the Ruby language. Any implementation that passes
+the full test corpus can claim bit-perfect MeshCore compatibility.
+
+## What's Here
+
+- **`spec/`** — RFC-style protocol specification in Markdown, covering every
+  layer from packet framing to cryptographic operations.
+- **`corpus/`** — JSON test vectors organized by protocol layer.
+  Each vector pairs a structured representation with its exact binary encoding,
+  enabling any implementation to verify encode and decode correctness.
+- **`tools/`** — Validation and generation utilities.
+
+## Test Vector Format
+
+Test vectors are JSON files. Binary data is represented as uppercase hex strings
+(whitespace allowed for readability). Each file contains an array of vectors in
+one of three modes:
+
+- **`encode_decode`** — Structured input paired with expected binary output.
+  Implementations MUST produce the given binary when encoding, and MUST recover
+  the given structure when decoding.
+- **`decode_only`** — Binary input with expected structured output. Used for
+  alternate valid encodings that an encoder need not produce but a decoder MUST
+  accept.
+- **`invalid`** — Binary input that MUST be rejected by a conforming decoder.
+
+See `corpus/schema/test-vector.schema.json` for the full schema.
+
+## Using the Corpus
+
+1. Parse each JSON file in `corpus/`.
+2. For `encode_decode` vectors: encode the `structured` form and compare to
+   `binary`; decode `binary` and compare to `structured`.
+3. For `invalid` vectors: attempt to decode `binary` and verify failure.
+
+No special tooling is required — just a JSON parser and your MeshCore
+implementation.
+
+## Project Status
+
+This project is under active development. The specification and corpus are being
+built from the [official MeshCore firmware](https://github.com/meshcore-dev/MeshCore)
+source code.
+
+## Protocol Versions
+
+The corpus covers all known MeshCore protocol versions. Each test vector file
+includes a `protocol_version` field. Version 1 (the current production version)
+has the most comprehensive coverage.
+
+## License
+
+MIT — see [LICENSE](LICENSE).
+
+## Contributing
+
+See [CONTRIBUTING.md](CONTRIBUTING.md).
+
+## Acknowledgments
+
+Based on the [MeshCore firmware](https://github.com/meshcore-dev/MeshCore) by
+the MeshCore developers. Protocol documentation derived from the official
+[MeshCore docs](https://docs.meshcore.io).