docs(website): the server half does not slice, and why

Found before writing any of it. §2.7.1 split the server extraction five ways by
feature; it does not divide, because two contract rules compose.

A mount prefix is claimed whole -- ownedByCore probes the live tier router and
registerRoutes validates single-segment prefixes -- and /admin/shard is one
386-line router carrying 25 routes across atlas, clilocs, shard-ops, visibility,
market and account links. Meanwhile a model cannot be shared across the boundary
(§5.1), so it moves with the last route that consumes it. Take the closure and
every prefix is in it: /public/atlas holds shardAtlas with /admin/shard, which
holds shardState/shardEvents/shardMarket with /public/shard, which holds
uoLinkConfig with /admin/uo-link, and shardClilocs/shardLinks with /player/shard.

Landing any one of the old slices alone would either strand core importing
modules/uo/ -- what acceptance criterion 2 forbids -- or delete routes core is
still serving.

Giving the admin routes their own prefixes would divide it and is rejected: it
changes API URLs, which §1.2 promises not to do, and not hypothetically. The
shipped Android app calls POST /api/v1/admin/shard/kick, /ban, /unban,
/broadcast and the three /pages routes.

So the table is now six slices: 0 the skeleton (done), 1 the whole server half
as ONE PR per repo structured as five commits along the old slice lines, 2-4 the
client halves, 5 close the phase. The client half is unaffected and still slices
cleanly -- the registry takes routes per area, with no prefix atomicity and no
shared models, the same asymmetry that let the two halves be separated at all.

Co-Authored-By: Claude <noreply@anthropic.com>

website/MODULE_API.md

@@ -866,7 +866,7 @@ to defend is *structural*: core must not name a module's files, import them, rou
 declare their symbols. It can talk about them in English.
 
 Core's UO-flavoured default copy is dealt with directly instead, as `MODULE_SYSTEM.md` §2.7.1's
-slice 8 — a rewrite with its own review, not an exemption.
+slice 4 — a rewrite with its own review, not an exemption.
 
 ### 5.3 Zero-line route manifest diff (CI, both repos)