feat(modules): interleave module nav, derive moderator confinement

Phase 2, PR 8 of docs/website/MODULE_SYSTEM.md 2.7 - the nav half PR 7
deferred, plus the two seams 1.4 and 1.5 asked for.

withModuleNav (client/src/modules/nav.js) merges an installed module's rows
into core's three navs BEFORE the admin-override merge, and that ordering is
the design. applyNavOverrides and buildPublicNav are keyed by `to` and drop
any key their base array does not declare, so rows appended after the merge
would be unorderable, unrelabellable and unhideable in Admin - Navigation.
Today's UO rows are all three of those things, so appending would make the
extraction a visible regression for anyone who has ever edited their nav.
Merging first means a module row is an ordinary row downstream: nothing in
navOverrides.js, NavEditor.jsx or the layouts knows a module exists.

MOD_PATHS is gone. Moderator visibility and the redirect that confines a
moderator both derive from each row's own `roles`, in the new plain-JS
lib/adminNav.js (plain so the DOM-less runner can reach it). Two rows move,
both toward what the server already permitted: Dashboard, whose roles had
always named moderator, and My Characters, which is ungated self-service.

That also fixes a defect predating the module system. The redirect was a
THIRD hardcoded list - three path prefixes against MOD_PATHS' five paths -
and they disagreed about /admin/houses, so a moderator who clicked Houses in
their own sidebar was bounced back to Moderation. The derived allow-list is
computed from the BASE nav, never the override-merged one: an override is
presentation and must not move an authorization boundary either way.

The feature seam (modules/features.jsx + modules/featureGate.js) resolves a
row's `feature` against the provider its OWN module registered, so the
namespace comes from the registration and no string carries a parsed prefix.
Core registers useShardFlags under the owner id `core` - the client twin of
registries.registerCore() - so the ten shard-gated header rows already run
through the seam and Phase 3 deletes a registration instead of rewriting
SiteHeader. Every unknown fails open: no provider, a null answer while a
fetch is in flight, or a junk return all show the link, because the server is
the gate and hiding a page from someone entitled to it is the worse mistake.

933 server tests (unchanged - this PR is client-only), 160 client tests
(+37). routes.manifest.json unchanged at 230 routes; the OpenAPI spec
regenerates byte-identical.

Re-ran the MODULE_API.md 7.7 browser smoke, since this is the seam that rule
exists for. A throwaway module registering nav in all three areas and a
provider granting one flag and withholding another: the row lands inside
core's Moderation group rather than an appended block, the withheld row does
not render, a moderator reaches both /admin/houses and the module's admin
page, and an admin can relabel a module row and have it persist and apply.
Zero CSP reports, zero console errors.

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

client/src/routes/admin/views/NavEditor.jsx

@@ -13,7 +13,8 @@ import { Loading, ErrorState } from '../../../components/PageState.jsx'
 import { api } from '../../../api/client.js'
 import { useAuth } from '../../../contexts/AuthContext.jsx'
 import { useSite } from '../../../contexts/SiteContext.jsx'
-import { useShardFeatures, canSee } from '../../../lib/useShardFeatures.js'
+import { withModuleNav } from '../../../modules/nav.js'
+import { useFeatureGate } from '../../../modules/features.jsx'
 import { buildNavRows, buildNavOverrides, buildPublicNav, buildPublicNavOverrides } from '../../../lib/navOverrides.js'
 import PublicNavTree from './PublicNavTree.jsx'
 import { parseJsonSetting } from '../../../lib/settingsJson.js'
@@ -244,7 +245,7 @@ export function Row({ row, id, destinations, destination, onDestination, onChang
 export default function NavEditor() {
   const { user } = useAuth()
   const { refresh: refreshSite } = useSite()
-  const shardFeatures = useShardFeatures()
+  const isVisible = useFeatureGate()
   const [tab, setTab] = useState('nav_public')
   // Per nav: the editable groups, the overrides as loaded (so a row this admin
   // cannot see survives their save), and whether a settings row exists at all.
@@ -255,25 +256,39 @@ export default function NavEditor() {
   const [saved, setSaved] = useState('')
   const [dirty, setDirty] = useState({})
 
-  // The palette: each base nav, filtered to what THIS admin can see (§8.1). The
-  // public nav's gates are the shard-feature ones; the admin nav's are roles.
-  // The player portal has no gates at all.
   // The nav as coded, unfiltered. The palette below is what this admin may EDIT;
   // this is what still EXISTS, and the two are different questions. Saving needs
   // both: an entry for a row their palette filtered out must be carried through
   // rather than reset, and only an entry for a route the code no longer declares
   // at all should be dropped.
-  const fullNavs = { nav_public: PUBLIC_NAV, nav_admin: ADMIN_NAV, nav_player: PLAYER_NAV }
+  //
+  // Each nav is the coded array with every installed module's rows already
+  // interleaved (modules/nav.js) — the same array the layout renders, which is
+  // what makes a module row editable here at all: the override merge is keyed by
+  // `to` and drops a key the base it is handed does not declare, so a nav built
+  // from core alone would silently discard every stored override on a module row
+  // the moment it was saved.
+  const fullNavs = useMemo(
+    () => ({
+      nav_public: withModuleNav(PUBLIC_NAV, 'public'),
+      nav_admin: withModuleNav(ADMIN_NAV, 'admin'),
+      nav_player: withModuleNav(PLAYER_NAV, 'player'),
+    }),
+    [],
+  )
 
+  // The palette: each base nav, filtered to what THIS admin can see (§8.1). Two
+  // gates, and neither is core's own opinion any more — `roles` on a row, and
+  // the owning module's answer for a row that names a `feature`.
   const palettes = useMemo(
     () => ({
-      nav_public: PUBLIC_NAV.filter((item) => !item.feature || canSee(shardFeatures, item.feature)),
-      nav_admin: ADMIN_NAV.map((g) => ({ ...g, items: g.items.filter((i) => navItemVisibleTo(i, user?.role)) })).filter(
-        (g) => g.items.length > 0,
-      ),
-      nav_player: PLAYER_NAV,
+      nav_public: fullNavs.nav_public.filter(isVisible),
+      nav_admin: fullNavs.nav_admin
+        .map((g) => ({ ...g, items: g.items.filter((i) => navItemVisibleTo(i, user?.role) && isVisible(i)) }))
+        .filter((g) => g.items.length > 0),
+      nav_player: fullNavs.nav_player.filter(isVisible),
     }),
-    [shardFeatures, user?.role],
+    [fullNavs, isVisible, user?.role],
   )
 
   useEffect(() => {