fix(favorites): Symbol-Adresse auch speichern, wenn nur der Browser sie laden kann

- API: ausdrueckliche iconUrl wird nur auf Form (http/https, <= 2048) geprueft
  und auch gespeichert, wenn der Server sie nicht abrufen kann; keine 422 mehr
- Erkennung: Seite mit Fehlerstatus, aber HTML mit <link rel=icon>, liefert
  diesen Verweis (docuvita); og:image einer Fehlerseite zaehlt nicht
- Kachel: Proxy -> iconUrl direkt im Browser (no-referrer, nur http/https) ->
  Origin-Favicon -> Buchstabe
- Meldung iconUrlUnreachable (de/en) entfernt, Hinweis zum Vorrang angepasst

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

apps/web/src/messages/en.json

@@ -380,10 +380,9 @@
       "viewModeLabel": "Switch view",
       "iconUrlPlaceholder": "Logo URL (optional)",
       "iconUploadLabel": "Upload custom icon",
-      "iconUploadHint": "PNG, JPEG, GIF, WebP, ICO or SVG, at most 512 KB. An uploaded icon takes precedence over the logo URL.",
+      "iconUploadHint": "PNG, JPEG, GIF, WebP, ICO or SVG, at most 512 KB. An uploaded icon takes precedence over the logo URL; a newly entered logo URL replaces it, though.",
       "iconUploadedHint": "A custom icon has been uploaded for this favorite.",
       "iconRemoveButton": "Remove uploaded icon",
-      "iconUrlUnreachable": "The image at this address could not be loaded. The site likely blocks automated requests (for example via a Cloudflare check) or is unreachable. Please upload the icon instead.",
       "iconTooLarge": "The file is too large – at most 512 KB is allowed.",
       "iconInvalidType": "Only PNG, JPEG, GIF, WebP, ICO or SVG images are allowed.",
       "iconUploadFailed": "The icon could not be uploaded."