refactor(tours): move non-component exports out of component files and split long hooks

Clears the client lint ratchet: helpers move to sibling .ts files for react-refresh, complex render paths get small helpers, floating promises are voided, the stage rail lets a stale request go during render, and the collections page reads the active list's tours and rights in ActiveCollectionTours. StageNumber is no longer exported.

client/src/utils/collectionAccess.ts

@@ -1,4 +1,4 @@
-import type { Collection } from '@trek/shared';
+import type { Collection, CollectionMember, CollectionRole } from '@trek/shared';
 
 /**
  * Whether the user may add to a list: their own, or a shared one where they
@@ -12,8 +12,24 @@ export function canAddToCollection(
   if (collection.is_owner !== false) return true;
   return (collection.members ?? []).some(
     (member) =>
-      member.user_id === userId &&
-      member.status === 'accepted' &&
-      (member.role === 'editor' || member.role === 'admin')
+      member.user_id === userId && member.status === 'accepted' && (member.role === 'editor' || member.role === 'admin')
   );
 }
+
+/**
+ * The user's role on a list: owner of their own, else the role a shared list
+ * gives them as a member, or null when they are neither.
+ */
+export function collectionRoleOf(
+  isOwner: boolean,
+  members: readonly Pick<CollectionMember, 'user_id' | 'is_owner' | 'role'>[],
+  userId: number | null | undefined
+): 'owner' | CollectionRole | null {
+  if (isOwner) return 'owner';
+  return members.find((member) => member.user_id === userId && !member.is_owner)?.role ?? null;
+}
+
+/** Whether a role may remove from a list: its owner or an admin of it. */
+export function canRemoveFromCollection(role: 'owner' | CollectionRole | null): boolean {
+  return role === 'owner' || role === 'admin';
+}