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/params/followList.ts

@@ -0,0 +1,5 @@
+import type { ParamMatcher } from '@sveltejs/kit';
+import type { FollowList } from '$lib/types';
+
+export const match = ((param: string): param is FollowList =>
+	param === 'followers' || param === 'following') satisfies ParamMatcher;