chore: add missing i18n keys in sidebar, assets, toolbox, dropdowns (#6622)

This PR 

- adds missing locale keys for 3D viewer toast strings, assets sidebar
labels, and node error keys
- cleans up the selection toolbox, media previews, node components, and
widget uploader to rely on `$t`/`st` (exposed to template scope at
compile time) instead of importing from `useI18n`.
- updates `eslint.config.ts` to teach the Intlify rule about the locale
layout

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6622-chore-add-missing-i18n-keys-in-sidebar-assets-toolbox-dropdowns-2a36d73d365081ae8694eb4f8ebb822a)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Alexander Brown <drjkl@comfy.org>

src/renderer/extensions/vueNodes/components/NodeHeader.vue

@@ -1,6 +1,6 @@
 <template>
   <div v-if="renderError" class="node-error p-4 text-sm text-red-500">
-    {{ $t('Node Header Error') }}
+    {{ st('nodeErrors.header', 'Node Header Error') }}
   </div>
   <div
     v-else