fix(frontend): align sharing UI with the merged role-grants backend

The merge brought in main's ReBAC→role-grants migration, which changed the
grant contract the Svelte sharing UI (branched before it) was written
against: GrantDto dropped `permission` and now carries an explicit `role`
(owner/editor/viewer/commenter/contributor), and the "admin" role was
renamed "owner". Left unchanged, the share UI derived roles from a
now-absent `permission` field and showed every member as "viewer".

- grants.ts: ShareRole is now viewer|editor|owner; Grant carries `role`
  (not `permission`); `roleFromPermissions` → `displayRole`, which collapses
  the unexposed commenter→viewer and contributor→editor.
- ShareDialog.svelte: read each subject's role directly (role-grants emits
  one row per subject); role picker exposes Owner instead of Admin.
- shared/+page.svelte (My Shares): same owner rename; role badges run
  through displayRole so server-only roles render sensibly.

Create/update already POST `role`, so only the read/display path and the
role literal needed fixing. npm run check, test:unit (36) and build pass.

frontend/src/routes/shared/+page.svelte

@@ -4,6 +4,7 @@
 	import { goto } from '$app/navigation';
 	import { onMount } from 'svelte';
 	import {
+		displayRole,
 		expiryToIso,
 		fetchMyShares,
 		notifyGrantRecipient,
@@ -33,12 +34,12 @@
 	];
 
 	const ROLES: { v: ShareRole; l: string; icon: string }[] = [
-		{ v: 'admin', l: t('share.role.canManage', 'Can manage'), icon: 'crown' },
+		{ v: 'owner', l: t('share.role.canManage', 'Can manage'), icon: 'crown' },
 		{ v: 'editor', l: t('share.role.canEdit', 'Can edit'), icon: 'pencil-alt' },
 		{ v: 'viewer', l: t('share.role.canView', 'Can view'), icon: 'eye' }
 	];
 	function roleMeta(r: string) {
-		return ROLES.find((x) => x.v === r) ?? ROLES[2];
+		return ROLES.find((x) => x.v === displayRole(r)) ?? ROLES[2];
 	}
 
 	let raw = $state<OutgoingGrantItem[]>([]);