docs: bound hemx mobile fit

Name when the mobile starter is the right suckless path and when to use an explicit native shell or island instead of pretending hemx is a general native UI framework.

req: ceremony/006

req: host/002

README.md

@@ -100,7 +100,9 @@ and integrate at explicit boundaries. req: laws/002 req: auth/001
   hemx-xtask -- app new --mobile PATH`. The starter carries a real app flow,
   typed host capabilities, command/event/projection recovery truth, and
   inspectable mobile release-kit commands without adding a native UI framework.
-  req: ceremony/006
+  Use it for Rust-owned hypermedia apps; use explicit native shells/islands for
+  heavy native UI, games, camera-heavy flows, deep OS integration, or complex
+  offline sync. req: ceremony/006 req: host/002
 - **PWA/offline/sync:** optional adapters may reuse generated targets/effects,
   but core hemx must not gain a mandatory client state graph or local app
   runtime. Local truth is commands/events/projections, not stored DOM patches or