Site title.

Read site_name from mkdocs.yml in the routing tests

The rename broke the routing suite, which is the suite working correctly: it
asserts page TITLES rather than status codes, precisely because a directory
listing also returns 200 and that is how cleanUrls:false once shipped past a
status-only suite. It caught the change.

What it should not have done is need a hand edit. The three title cases pinned
the literal string Immersive Fusion Docs, so the brand lived in a test file as
well as in mkdocs.yml, and a rename had to remember to visit both. It did not.
Renaming the site broke CI before it broke anything a reader could see, which
is the good version of this failure, but the next one might not be.

Now read from mkdocs.yml at import. The assertion still does its real job,
which is proving the response is a rendered page and not a directory listing,
and a directory listing will not carry the site name whatever it is called.

This is the rule check-redirect-parity.py already states for the redirect maps,
that there is exactly one reader of mkdocs.yml because a second one that
normalizes differently is how they drift apart. Same reason here.

Verified: the module imports, SITE_NAME reads back as DeepCube Docs, and the
three cases resolve to it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>