Let users browse followers and following lists

Following lists are public; followers are visible to the user and to mutual followers.
Adds GET /users/{id}/followers and /following, exposes isFollowing and canViewFollowers
on the profile, and returns isFollowedByViewer from user search so the web player no
longer calls /is-following per user.

web-player/src/lib/components/ui/media/UserRow.svelte

@@ -0,0 +1,28 @@
+<script lang="ts">
+	import ListRow from './ListRow.svelte';
+	import Avatar from './Avatar.svelte';
+	import FollowButton from './FollowButton.svelte';
+
+	interface Props {
+		user: {
+			id: string;
+			name: string;
+			profilePictureUrl: string | null;
+			isFollowedByViewer: boolean;
+		};
+		canFollow?: boolean;
+	}
+
+	let { user, canFollow = false }: Props = $props();
+</script>
+
+<div class="flex items-center gap-3">
+	<ListRow title={user.name} href="/user/{user.id}" size="lg" class="min-w-0 flex-1">
+		{#snippet art()}
+			<Avatar name={user.name} src={user.profilePictureUrl} size="md" />
+		{/snippet}
+	</ListRow>
+	{#if canFollow}
+		<FollowButton following={user.isFollowedByViewer} userId={user.id} class="shrink-0" />
+	{/if}
+</div>