feat: improve bookmark dialog UX with distinct modes, inline validation, and accessibility

Refine bookmark create/edit and group create/edit dialogs to enterprise
quality: distinct titles per mode (Add bookmark vs Edit bookmark), URL
preview when creating, inline field validation with aria-invalid instead
of toast-only errors, loading spinner on submit, compact inline
new-group link, human-readable icon picker aria-labels, and aria-pressed
on selected icons.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

modules/bookmarks/i18n/default_de.json

@@ -39,5 +39,29 @@
   "Edit group": "Gruppe bearbeiten",
   "Group updated": "Gruppe aktualisiert",
   "Group name is required": "Gruppenname ist erforderlich",
-  "Maximum groups reached": "Maximale Anzahl an Gruppen erreicht"
+  "Maximum groups reached": "Maximale Anzahl an Gruppen erreicht",
+  "Add bookmark": "Lesezeichen hinzufügen",
+  "Saving...": "Speichern...",
+  "Create group": "Gruppe erstellen",
+  "Bookmarking this page:": "Lesezeichen für diese Seite:",
+  "Icon: Home": "Zuhause",
+  "Icon: People": "Personen",
+  "Icon: Person": "Person",
+  "Icon: Folder": "Ordner",
+  "Icon: Document": "Dokument",
+  "Icon: Settings": "Einstellungen",
+  "Icon: Security": "Sicherheit",
+  "Icon: Chart": "Diagramm",
+  "Icon: Mail": "E-Mail",
+  "Icon: Calendar": "Kalender",
+  "Icon: Clock": "Uhr",
+  "Icon: Star": "Stern",
+  "Icon: Heart": "Herz",
+  "Icon: Flag": "Flagge",
+  "Icon: Bookmark": "Lesezeichen",
+  "Icon: Location": "Standort",
+  "Icon: Lightning": "Blitz",
+  "Icon: Database": "Datenbank",
+  "Icon: Globe": "Globus",
+  "Icon: Code": "Code"
 }