fix: no user ever had a username, so people search found nobody

Root cause of "still cannot find users": username was optional in
better-auth's schema and no signup form or settings page ever set it,
but search/profile/follow all key on username, not user id. Every
account now gets a unique one auto-generated (from name/email) in the
user.create.before hook — covers email/password and OAuth signups.
Added a one-off db:backfill-usernames script for accounts created
before this fix and ran it against the current database.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/lib/changelog.ts

@@ -1,5 +1,5 @@
 // Mirrors CHANGELOG.md at the repo root — update both together.
-export const APP_VERSION = "0.13.0";
+export const APP_VERSION = "0.13.1";
 
 export type ChangelogEntry = {
   version: string;
@@ -11,6 +11,13 @@ export type ChangelogEntry = {
 };
 
 export const CHANGELOG: ChangelogEntry[] = [
+  {
+    version: "0.13.1",
+    date: "2026-07-13 17:25",
+    fixed: [
+      "People search never found anyone, for anyone — there was no signup or settings flow that ever set a username, and search (along with profiles and follow) requires one. Every account now gets one automatically on signup; existing accounts were backfilled.",
+    ],
+  },
   {
     version: "0.13.0",
     date: "2026-07-13 15:37",