docs(blog): reframe Lanhu audit as prompt tutorial

Rewrite the Lanhu precision-audit article around reusable prompt templates, including source-of-truth constraints, box-model ledgers, edge and gap tables, list contracts, token mapping, runtime image checks, and post-patch review prompts.

Tested: git diff --check

Tested: ruby /opt/homebrew/lib/ruby/gems/3.4.0/gems/bundler-4.0.3/exe/bundle exec jekyll build

Author: Donglu