cleanup plugin installer and store wiring

Align plugin installer and plugin settings UI with the frontend component/store patterns.

- compose plugin_installer main.html from install-index/install-git/install-zip components instead of duplicating tab markup
- restore shared plugin window CSS in main.html while keeping tab content delegated to dedicated components
- replace remaining direct cross-store/template calls with store methods and module imports
- route installer screenshot opening through pluginInstallStore and rewire plugin init opening through pluginListStore
- extract settings/plugins subsection logic from inline x-data into a dedicated store-backed context
- remove touched plugin/settings Alpine.store lookups in favor of explicit store imports
- fix advanced toggle behavior so the switch can create a rule immediately for the selected scope
- restore installer success/result state used by the git/zip tab UIs

plugins/plugin_installer/webui/install-index.html

@@ -9,8 +9,7 @@
     <div x-data>
         <template x-if="$store.pluginInstallStore">
             <div class="pi-browse-shell"
-                 x-init="$store.pluginInstallStore.resetIndex(); $store.pluginInstallStore.fetchIndex()"
-                 x-destroy="$store.pluginInstallStore.refreshPluginList()">
+                 x-create="$store.pluginInstallStore.resetIndex(); $store.pluginInstallStore.fetchIndex()">
 
                 <section class="pi-browse-hero">
                     <div class="pi-browse-copy">