chore: update/make more clear connect flow

src/config/instances.ts

@@ -98,6 +98,11 @@ export function upsertInstance(url: string, name?: string): Instance {
   return inst;
 }
 
+/** Clear a backend's stored session without forgetting the instance itself. */
+export function clearInstanceAuth(id: string): void {
+  localStorage.removeItem(scopedKey('auth', id));
+}
+
 /** Remove a backend and wipe every scoped key it owns. */
 export function removeInstance(id: string): void {
   writeRegistry(readRegistry().filter((i) => i.id !== id));