feat(frontend): add expandable text component for long fields

Adds ExpandableText.svelte which clamps text to 10 lines and shows a
toggle button only when the content actually overflows. Applied to the
summary and transcription fields on the document detail page.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/messages/de.json

@@ -238,5 +238,7 @@
 	"admin_system_backfill_heading": "Verlaufsdaten auffüllen",
 	"admin_system_backfill_description": "Erstellt einen initialen Verlaufseintrag für alle Dokumente, die noch keinen Verlauf haben (z.B. importierte Dokumente). Dadurch werden beim nächsten Bearbeiten nur die tatsächlich geänderten Felder hervorgehoben.",
 	"admin_system_backfill_btn": "Jetzt auffüllen",
-	"admin_system_backfill_success": "{count} Dokumente wurden aufgefüllt."
+	"admin_system_backfill_success": "{count} Dokumente wurden aufgefüllt.",
+	"comp_expandable_show_more": "Mehr anzeigen",
+	"comp_expandable_show_less": "Weniger anzeigen"
 }

frontend/messages/en.json

@@ -238,5 +238,7 @@
 	"admin_system_backfill_heading": "Backfill history data",
 	"admin_system_backfill_description": "Creates an initial history entry for all documents that do not have one yet (e.g. imported documents). This ensures that future edits only highlight actually changed fields.",
 	"admin_system_backfill_btn": "Backfill now",
-	"admin_system_backfill_success": "{count} documents were backfilled."
+	"admin_system_backfill_success": "{count} documents were backfilled.",
+	"comp_expandable_show_more": "Show more",
+	"comp_expandable_show_less": "Show less"
 }

frontend/messages/es.json

@@ -238,5 +238,7 @@
 	"admin_system_backfill_heading": "Completar datos de historial",
 	"admin_system_backfill_description": "Crea una entrada de historial inicial para todos los documentos que aún no tienen ninguna (p.ej. documentos importados). Así, en la próxima edición solo se resaltarán los campos realmente modificados.",
 	"admin_system_backfill_btn": "Completar ahora",
-	"admin_system_backfill_success": "{count} documentos fueron completados."
+	"admin_system_backfill_success": "{count} documentos fueron completados.",
+	"comp_expandable_show_more": "Mostrar más",
+	"comp_expandable_show_less": "Mostrar menos"
 }