fix(branding): allow larger square favicons

The upload never enforced 32x32 - only the help text recommended it,
which misled admins. Update the EN/DE guidance to recommend a larger
square image (512x512) and raise the favicon upload cap 1MB -> 2MB so
high-resolution PNGs fit comfortably.

frontend/src/i18n/locales/de.json

@@ -1708,7 +1708,7 @@
     "currentFavicon": "Aktuelles Favicon",
     "uploadFavicon": "Favicon hochladen",
     "removeFavicon": "Favicon entfernen",
-    "faviconHelp": "PNG- oder ICO-Format, empfohlene Größe: 32x32px",
+    "faviconHelp": "PNG- oder ICO-Format. Bitte ein quadratisches Bild verwenden – empfohlen sind 512×512px für eine scharfe Darstellung auf hochauflösenden Bildschirmen; kleinere Größen funktionieren ebenfalls.",
     "watermarkSettings": "Wasserzeichen-Einstellungen",
     "enableWatermarks": "Wasserzeichen aktivieren",
     "watermarkHelp": "Fügen Sie Ihren Firmennamen als Wasserzeichen auf heruntergeladenen Fotos hinzu",

frontend/src/i18n/locales/en.json

@@ -1297,7 +1297,7 @@
     "currentFavicon": "Current favicon",
     "uploadFavicon": "Upload Favicon",
     "removeFavicon": "Remove Favicon",
-    "faviconHelp": "PNG or ICO format, recommended size: 32x32px",
+    "faviconHelp": "PNG or ICO format. Use a square image — 512×512px is recommended for crisp display on high-resolution screens; smaller sizes work too.",
     "watermarkSettings": "Watermark Settings",
     "enableWatermarks": "Enable Watermarks",
     "watermarkHelp": "Add your company name as a watermark on downloaded photos",