feat(social): add friends, private chats, inbox and music sharing

apps/web/src/test/e2eBridge.ts

@@ -10,6 +10,10 @@ export function installE2EFetch() {
     makeUser('mobile-admin', 'admin', { reviews_uploads: true }),
     makeUser('moderator', 'moderator', { reviews_uploads: true }),
   ]);
+  // A ready conversation lets browser tests exercise messages and music sharing.
+  const alice = [...api.users.values()].find(u => u.username === 'alice')!;
+  const friend = [...api.users.values()].find(u => u.username === 'moderator')!;
+  api.friendships.set([alice.id, friend.id].sort().join(':'), { sender: friend.id, accepted: true });
   const orig = window.fetch.bind(window);
   window.fetch = async (input, init) => {
     const req = new Request(input, init);