feat: persistent app install state across navigation (#9)

Move installingApps from local refs in Marketplace/Discover to the
global server store. Install progress now persists when navigating
between views. My Apps shows installing overlay with progress bar
for apps being installed from the Marketplace.

Changes:
- server.ts: add installingApps Map + helpers to store
- Marketplace.vue: use store's installingApps instead of local ref
- Discover.vue: same
- Apps.vue: pass isInstalling + installProgress to AppCard
- AppCard.vue: add amber installing overlay with progress bar

522 tests pass, vue-tsc clean.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

neode-ui/src/views/Apps.vue

@@ -101,6 +101,8 @@
         :index="index"
         :show-stagger="showStagger"
         :is-loading="!!actions.loadingActions.value[id as string]"
+        :is-installing="serverStore.isInstalling(id as string)"
+        :install-progress="serverStore.installingApps.get(id as string)"
         :is-uninstalling="actions.uninstallingApps.value.has(id as string)"
         @go-to-app="goToApp"
         @launch="launchApp"
@@ -141,6 +143,7 @@ import { computed, ref, watch, onMounted, onBeforeUnmount } from 'vue'
 import { useRouter, useRoute, RouterLink } from 'vue-router'
 import { useI18n } from 'vue-i18n'
 import { useAppStore } from '@/stores/app'
+import { useServerStore } from '@/stores/server'
 import { useAppLauncherStore } from '@/stores/appLauncher'
 import type { PackageDataEntry } from '@/types/api'
 import AppCard from './apps/AppCard.vue'
@@ -155,6 +158,7 @@ const { t } = useI18n()
 const router = useRouter()
 const route = useRoute()
 const store = useAppStore()
+const serverStore = useServerStore()
 const actions = useAppsActions()
 
 // Only stagger-animate on first mount