fix(ui): minor icon inconsistencies and "no missing files" translation (#3837)

* chore(ui): Fix minor inconsistencies

1. The icons in the user menu are a mix of MUI and react-icons. Move them all to react-icons, and use a standard size (24px)
2. On missing files page, provide a custom Empty component that just removes 'yet'

* use RA's builtin support for custom empty message

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>
Co-authored-by: Deluan <deluan@navidrome.org>

resources/i18n/pt.json

@@ -229,6 +229,7 @@
     },
     "missing": {
       "name": "Arquivo ausente |||| Arquivos ausentes",
+      "empty": "Nenhum arquivo ausente",
       "fields": {
         "path": "Caminho",
         "size": "Tamanho",