CI: PR Preview URL detection failure

## What happened

Scenario from PR preview runs in https://github.com/influxdata/docs-v2/pull/7513:

1. PR Preview didn't detect a backtick-quoted, valid URL path in the body--the run log shows the environment setup completed before the detector failed.
2. I unquoted the path and saved the body.
3. PR Preview ran automatically and correctly discovered the path.
4. PR preview scaffolded the preview, but didn't render the API page - returned a `404`.

## What I expect to happen

1. PR Preview should fail fast, before setting up the environment, when no path or URL is detected.
2. PR Preview should detect delimited, quoted, or backtick-quoted URLs in the PR body
3. PR preview should `build:api-docs` for previewing API reference pages

Start by reproducing the PR Preview scenario from pull request 7513 and inspect the detector and environment-setup steps shown in the run log. Trace how PR body paths are parsed and how API preview pages are built, then verify quoted URL detection, fail-fast behavior, and successful API rendering.

Written by the indexing model from the issue text.