refactor(settings/branding): two side-by-side upload cards via barrier forms

Branding now follows the tenant-logos pattern: four hidden barrier forms
(logo upload + delete, favicon upload + delete) declared once at the top
and two file-upload partials placed side-by-side inside a grid, hooked
to their forms via the HTML5 form="..." attribute. The redundant
preview wrapper above each upload is gone — the file-upload partial
already renders the current image, replace/delete buttons and metadata.
The favicon hint moves from a separate blockquote into the upload's
hint field so it sits in the dropzone where it matters.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

i18n/default_de.json

@@ -820,6 +820,7 @@
   "Please select a primary tenant": "Bitte einen Hauptmandanten auswählen",
   "Please select at least one tenant": "Bitte mindestens einen Mandanten auswählen",
   "Please verify your email first": "Bitte bestätige zuerst deine E-Mail",
+  "PNG, square recommended (icons are center-cropped)": "PNG, quadratisch empfohlen (Icons werden zentriert beschnitten)",
   "Policy": "Regel",
   "Port": "Port",
   "POST Parameters": "POST-Parameter",
@@ -886,6 +887,8 @@
   "Remove permission": "Berechtigung entfernen",
   "Remove role": "Rolle entfernen",
   "Remove selected file": "Ausgewaehlte Datei entfernen",
+  "Remove the app logo?": "App-Logo entfernen?",
+  "Remove the favicon?": "Favicon entfernen?",
   "Replace": "Ersetzen",
   "Request": "Anfrage",
   "Request details": "Request-Details",