Implement plugin dynamic settings routes architecture

Plugins can now register their settings pages dynamically via get_settings_routes()
hook, eliminating hardcoded imports that break lean builds.

Backend:
- Add get_settings_routes() hook to BasePlugin (shopdb/plugins/base.py)
- Implement in ComputersPlugin for Operating Systems management
- Add /api/plugins/settings-routes endpoint to expose plugin routes

Frontend:
- ModelCatalogHub fetches plugin routes and dynamically adds them via router.addRoute()
- Tabs render dynamically from pluginTabs ref
- Components lazy-load when clicked

Benefits:
- Lean builds work without manual route exclusions
- Plugins self-contain their UI extensions
- No core code changes needed when adding plugin settings pages
- Follows plugin architecture best practices

Fixes TODO from commit a03fd3de4f

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

frontend/src/views/settings/ModelCatalogHub.vue

@@ -27,14 +27,16 @@
       >
         Models
       </router-link>
-      <!-- TODO: Operating Systems tab should be added by computers plugin -->
-      <!-- <router-link
-        :to="{ name: 'model-catalog-os' }"
+      <!-- Plugin-contributed tabs loaded dynamically -->
+      <router-link
+        v-for="tab in pluginTabs"
+        :key="tab.name"
+        :to="{ name: tab.name }"
         class="tab"
-        :class="{ active: $route.name === 'model-catalog-os' }"
+        :class="{ active: $route.name === tab.name }"
       >
-        Operating Systems
-      </router-link> -->
+        {{ tab.tab }}
+      </router-link>
     </div>
 
     <div class="tab-content">
@@ -44,13 +46,37 @@
 </template>
 
 <script setup>
-import { onMounted } from 'vue'
+import { ref, onMounted } from 'vue'
 import { useRoute, useRouter } from 'vue-router'
+import axios from 'axios'
 
 const route = useRoute()
 const router = useRouter()
+const pluginTabs = ref([])
+
+onMounted(async () => {
+  // Fetch plugin-contributed settings routes
+  try {
+    const response = await axios.get('/api/plugins/settings-routes')
+    if (response.data && response.data.data) {
+      // Filter for model-catalog hub routes
+      pluginTabs.value = response.data.data.routes.filter(r => r.hub === 'model-catalog')
+
+      // Dynamically register routes for plugin tabs
+      pluginTabs.value.forEach(tab => {
+        if (!router.hasRoute(tab.name)) {
+          router.addRoute('model-catalog', {
+            path: tab.path,
+            name: tab.name,
+            component: () => import(`../../${tab.component}`)
+          })
+        }
+      })
+    }
+  } catch (error) {
+    console.error('Failed to load plugin settings routes:', error)
+  }
 
-onMounted(() => {
   // Redirect to vendors tab if no child route
   if (route.name === 'model-catalog') {
     router.replace({ name: 'model-catalog-vendors' })