The Federation and Runs help buttons opened the architecture doc:
federation.md/runs.md existed as assets but had no _DocEntry, so
showFaiDoc resolved the unknown slug to _kDocs.first. Register both
(onWelcome: false, so they don't clutter the newcomer grid but are
reachable), split the Welcome grid onto the curated subset, and make
the unknown-slug fallback assert in debug instead of silently opening
the wrong topic.
Guard (no-bugfix-without-a-guard): doc_help_wiring_test.dart scans
lib/ for every showFaiDoc('slug') call and asserts each has a
registered entry AND both assets/docs/<slug>[_de].md files. Exposes
kKnownDocSlugs for the test.
Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>
