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>

eslint.config.ts

@@ -33,7 +33,18 @@ const settings = {
       ],
       noWarnOnMultipleProjects: true
     })
-  ]
+  ],
+  'vue-i18n': {
+    localeDir: [
+      {
+        pattern: './src/locales/**/*.json',
+        localeKey: 'path',
+        localePattern:
+          /^\.?\/?src\/locales\/(?<locale>[A-Za-z0-9-]+)\/.+\.json$/
+      }
+    ],
+    messageSyntaxVersion: '^9.0.0'
+  }
 } as const
 
 const commonParserOptions = {