feat(navigator): empty-state + skeleton views, fix double search fetch (P4 wave 1a)

Visual polish, first wave:
- NavigatorEmptyStateView: replaces the bare "No rooms found" text with a
  centered icon + message + a Create-room CTA. Reuses existing i18n keys
  (navigator.search.returned.no.results / .roomsettings.moderation.none /
  .createroom.create) so no new localization entries are needed.
- NavigatorSearchSkeletonView: animate-pulse placeholder rows shown while a
  search is in flight and no result is cached yet (matches the HK dashboard
  skeleton pattern). Replaces the NitroCard.Content spinner overlay for the
  result list.

Bug fix bundled in: NavigatorSearchView called useNavigatorSearch() a second
time purely to read searchResult for its input-sync effect. Since the hook is
not a useBetween singleton, that registered a duplicate NavigatorSearchEvent
listener AND fired a duplicate NavigatorSearchComposer on every search.
NavigatorView now owns the single useNavigatorSearch() call and passes
searchResult to NavigatorSearchView via prop.

Test maintenance: useNavigatorSearch.test.tsx was written for the original
useNitroQuery implementation, which upstream reverted (05d71dd1) to
useMessageEvent + useState. Removed the dead QueryClient scaffolding, fixed
case 1 (assert no fetch starts with empty tab), dropped case 7 (the query
invalidator no longer exists). 6 cases, all green.

Full suite 471/471. Typecheck: only the environmental renderer-mismatch
errors (soundboard / rare-values / floorplan APIs absent from the linked
renderer), none in navigator files.

src/components/navigator/NavigatorView.tsx

@@ -14,8 +14,10 @@ import { NavigatorRoomCreatorView } from './views/NavigatorRoomCreatorView';
 import { NavigatorRoomInfoView } from './views/NavigatorRoomInfoView';
 import { NavigatorRoomLinkView } from './views/NavigatorRoomLinkView';
 import { NavigatorRoomSettingsView } from './views/room-settings/NavigatorRoomSettingsView';
+import { NavigatorEmptyStateView } from './views/search/NavigatorEmptyStateView';
 import { NavigatorSearchResultView } from './views/search/NavigatorSearchResultView';
 import { NavigatorSearchSavesResultView } from './views/search/NavigatorSearchSavesResultView';
+import { NavigatorSearchSkeletonView } from './views/search/NavigatorSearchSkeletonView';
 import { NavigatorSearchView } from './views/search/NavigatorSearchView';
 
 export const NavigatorView: FC<{}> = props =>
@@ -132,7 +134,7 @@ export const NavigatorView: FC<{}> = props =>
                             <FaPlus className="fa-icon" />
                         </NitroCard.TabItem>
                     </NitroCard.Tabs>
-                    <NitroCard.Content isLoading={ isFetching }>
+                    <NitroCard.Content>
                         { !isCreatorOpen &&
                             <div className="flex h-full overflow-hidden gap-2">
                                 { isOpenSavesSearches &&
@@ -140,13 +142,13 @@ export const NavigatorView: FC<{}> = props =>
                                         <NavigatorSearchSavesResultView searches={ navigatorSearches || [] } />
                                     </div> }
                                 <div className="flex flex-col w-full overflow-hidden gap-2">
-                                    <NavigatorSearchView />
+                                    <NavigatorSearchView searchResult={ searchResult } />
                                     <div ref={ elementRef } className="flex flex-col flex-1 min-h-0 overflow-auto gap-2">
+                                        { (isFetching && !searchResult) &&
+                                            <NavigatorSearchSkeletonView /> }
                                         { searchResult && searchResult.results.map((result, index) => <NavigatorSearchResultView key={ index } searchResult={ result } />) }
                                         { searchResult && (!searchResult.results || searchResult.results.length === 0) &&
-                                            <div className="nitro-card-panel px-3 py-2 text-sm text-muted">
-                                                { LocalizeText(searchResult.code === 'myworld_view' ? 'navigator.roomsettings.moderation.none' : 'navigator.search.returned.no.results') }
-                                            </div> }
+                                            <NavigatorEmptyStateView code={ searchResult.code } onCreateRoom={ () => useNavigatorUiStore.getState().openCreator() } /> }
                                     </div>
                                     <Flex className="nitro-card-divider pt-2 border-t gap-2">
                                         <Flex pointer alignItems="center" justifyContent="center"