Markdown Docs Corpus Discovery

Perform initial reconnaissance of a Markdown documentation corpus (a git repo or folder of .md/.mdx files). Produces a corpus inventory, repository structure map, and recommendations for deeper analysis. Use when the user wants to understand "what documentation do we have," audit or inventory a Markdown docs repository, get a first-pass map of a docs-as-code corpus before deeper work, or asks "what's in our docs," "how mature is our documentation," "audit our docs repo," or "give me a corpus overview." Scoped to Markdown only — a poor fit if the corpus is primarily Confluence exports, Word docs, PDFs, or HTML. Does not classify documents into types or infer a schema — tha…