fix: resolve index-style and template slugs in the docs MCP server

[philip]

Overview

Fix slug resolution in the DevHub docs MCP server. get_doc_resource matched only bare docs slugs, so a slug copied from list_docs_resources (a full URL, a docs/ prefix, or a trailing .md) and any template or recipe page returned not found. This normalizes the slug and routes template, recipe, and solution pages through a shared renderDetailMarkdown helper, now used by the MCP route, the /api/markdown route, and the static-artifact build script, so all three return identical markdown.

Reported through DevHub agent feedback.

Verified end to end over HTTP against a local server: index-style slugs and template/recipe pages resolve, and path traversal is still rejected.

This pull request and its description were written by Isaac.

[thisistonydang]

Tony's agent: I reproduced an issue with the section overview URLs returned by list_docs_resources.

Calling get_doc_resource with https://developers.databricks.com/templates.md returns the docs article titled “What are templates?” instead of the full template catalog.

Calling it with https://developers.databricks.com/solutions.md returns “Doc page not found”.

Individual detail URLs, such as https://developers.databricks.com/templates/genie-conversational-analytics.md, work correctly.

The parser only recognizes templates/ and solutions/ with a trailing slash. It should also recognize the bare templates and solutions paths after removing the .md suffix. Please add tests for both overview URLs.