fix(settings): hide the built-in type picker when setting up a plugin

The plugin Set up form reused the new-source editor, which always showed
an Indexer type select listing only torznab and newznab. Changing it
saved a torznab feed under the plugin's name, which is how a MyAnonaMouse
feed ended up pointed at the tracker's website.

client/src/features/settings/RequestIndexersPanel.vue

@@ -727,7 +727,11 @@ function handleTestCurrent() {
 
       <template #default>
         <SettingsSection :title="t('settings.system.requests.sections.connection')">
-          <SettingsField v-if="draft.id === null" :label="t('settings.system.requests.indexers.fields.type')" input-id="indexer-type">
+          <SettingsField
+            v-if="draft.id === null && isBuiltInAdapter(draft.adapterType)"
+            :label="t('settings.system.requests.indexers.fields.type')"
+            input-id="indexer-type"
+          >
             <template #default="{ describedBy }">
               <select
                 id="indexer-type"

client/src/features/settings/__tests__/RequestIndexersPanel.spec.ts

@@ -695,6 +695,16 @@ describe('RequestIndexersPanel', () => {
       expect(sheet().querySelector<HTMLInputElement>('#indexer-name')?.value).toBe('Demo Tracker')
     })
 
+    /** The plugin already settles the type, and switching it here would save a torznab feed under the plugin's name. */
+    it('does not offer the built-in type picker when setting up a plugin', async () => {
+      const wrapper = await mountPanel({ adapters: [descriptor(), PLUGIN] })
+
+      await clickInPanel(wrapper, 'Set up')
+
+      expect(sheet().querySelector('#indexer-name')).not.toBeNull()
+      expect(sheet().querySelector('#indexer-type')).toBeNull()
+    })
+
     /** Once something uses it, it is that source, and a second row for it would be a duplicate. */
     it('stops listing it separately once a source uses it', async () => {
       const wrapper = await mountPanel({