homepage: AI section to the bottom; model-only AI descriptions

The user page now orders Web Apps, Media Library Apps, AI — the models sit
at the bottom, below the apps people click. The AI card and /docs#models
descriptions drop the infrastructure (runtimes, GPUs, tensor parallelism,
draft heads) in favor of what users care about: the hosted model, its
size, the context/parallel capacity, and what it's good at.

tests/homepage_pages.bats

@@ -41,6 +41,10 @@ setup() {
     grep -q "repeat(auto-fill" "$BASE/style.css"
 }
 
+@test "the user page keeps the AI section at the bottom" {
+    grep -q "user: \['Web Apps', 'Media Library Apps', 'AI'\]" "$BASE/app.js"
+}
+
 @test "WIP badges distinguish open from closed work" {
     grep -q "WIP: OPEN" "$BASE/app.js"
     grep -q "WIP: CLOSED" "$BASE/app.js"