rag-architect: hardcoded API key placeholder in cohere.Client example

[specterslient95-lgtm]

Problem

The skills/rag-architect/SKILL.md reranking example uses:

co = cohere.Client("YOUR_API_KEY")

The surrounding skill does not show a safer secret-loading pattern for this provider.

Impact

This can teach users or agents to paste secrets directly into source code. In a RAG implementation skill, credential handling examples should consistently model environment-variable or secret-manager usage.

Suggested fix

Replace the placeholder with an environment-based pattern, for example:

import os
import cohere

co = cohere.Client(os.environ["COHERE_API_KEY"])

Also add a short note not to commit provider API keys.