fix(frontend): simplify collections view and restore invite access

Unify collections and shared items under a single Collections tab while keeping Archive separate, and fix card layering so menus render correctly. Restore invite discoverability by adding navbar access to /invites and add missing i18n keys to prevent raw key labels in collections/invites UI.

frontend/src/locales/sv.json

@@ -1038,6 +1038,7 @@
 	"invites": {
 		"accept": "Acceptera",
 		"accept_failed": "Det gick inte att acceptera inbjudan",
+		"fetch_failed": "Det gick inte att hämta inbjudningar",
 		"accepted": "Bjuda in accepterad",
 		"by": "av",
 		"decline": "Nedgång",
@@ -1081,7 +1082,8 @@
 	},
 	"common": {
 		"show_less": "Dölj detaljer",
-		"show_more": "Visa mer"
+		"show_more": "Visa mer",
+		"refresh": "Uppdatera"
 	},
 	"currencies": {
 		"AED": "UAE Dirham",