Normalize cross-repo links to absolute GitHub URLs

Each SDK is its own GitHub repository, so relative paths like
../spec/docs/draft-arcp-1.1.md don't resolve when the README is
viewed on github.com. Switching to absolute spec URLs makes the
links work in both the GitHub UI and any rendered docs surface.
A few stale references to removed files (RFC-0001-v2.md, PLAN.md)
and snake_case sample dirs are tidied along the way.

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

Author: nficano

README.md

@@ -2,10 +2,10 @@
 
 [![License: Apache-2.0](https://img.shields.io/badge/license-Apache--2.0-blue)](LICENSE)
 [![Python ≥ 3.11](https://img.shields.io/badge/python-%E2%89%A53.11-blue)](pyproject.toml)
-[![ARCP v1.1](https://img.shields.io/badge/arcp-v1.1-blue)](../spec/docs/draft-arcp-1.1.md)
+[![ARCP v1.1](https://img.shields.io/badge/arcp-v1.1-blue)](https://github.com/agentruntimecontrolprotocol/spec/blob/main/docs/draft-arcp-1.1.md)
 
 Reference implementation of ARCP v1.1 for Python. The wire is defined
-in [`../spec/docs/draft-arcp-1.1.md`](../spec/docs/draft-arcp-1.1.md);
+in [the ARCP spec](https://github.com/agentruntimecontrolprotocol/spec/blob/main/docs/draft-arcp-1.1.md);
 this SDK is one of eleven implementations tracked in the workspace's
 per-SDK conformance pages.