test(webserve_e2e): stop asserting 200 on a docs root with no index

The 4ec34d1c repin was right about the redirect and wrong about what it
lands on. It asserted GET /llms.txt/docs/ == 200; measured at 71caedd4 that
is 404, and the 404 is correct: this fixture's docs dir contains cli/
reference.md and the root-file labels, and no index.html. A docs root
without one is a 404 by design -- webserve.rs:1028-1033 writes index.html
precisely in order to get 200 at /local/docs/.

So the assertion pinned index-presence, which is not this case's subject.
The redirect (302 + Location) is still asserted, and the following line
already fetches /llms.txt/docs/llms.txt and compares bytes -- a real leaf
fetched THROUGH the redirect target, which is stronger evidence that the
target is live than a status on the directory root ever was.

Measured at 71caedd4, producer 3: the case now clears the old :266 and the
new 302/Location pair, and failed only on this line. The four sibling cases
stayed green, so the repin's blast radius is the one case.

UNCOMPILED AND UNRUN at commit time: written outside the window, measured
in the next one.

Co-authored by: hertz
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GY7rT7iPXEDNb7FN18WX1K