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>

packages/db/package.json

@@ -13,6 +13,7 @@
     "migrate": "drizzle-kit migrate",
     "studio": "drizzle-kit studio",
     "seed": "tsx src/seed.ts",
+    "backfill-usernames": "tsx src/backfill-usernames.ts",
     "typecheck": "tsc --noEmit"
   },
   "dependencies": {

packages/db/src/backfill-usernames.ts

@@ -0,0 +1,51 @@
+import { db } from "./client";
+import { users } from "./schema";
+import { eq, isNull } from "drizzle-orm";
+
+// Mirrors apps/web/lib/username.ts's slugify — duplicated rather than shared
+// since packages/db doesn't depend on apps/web. Kept intentionally simple.
+function slugify(seed: string): string {
+  const base = seed
+    .split("@")[0]!
+    .toLowerCase()
+    .replace(/[^a-z0-9_]/g, "")
+    .slice(0, 20);
+  return base.length >= 3 ? base : `${base}user`.slice(0, 20);
+}
+
+async function backfillUsernames() {
+  const rows = await db.query.users.findMany({
+    where: isNull(users.username),
+    columns: { id: true, name: true, email: true },
+  });
+
+  console.log(`${rows.length} user(s) missing a username.`);
+
+  const taken = new Set(
+    (await db.query.users.findMany({ columns: { username: true } }))
+      .map((u) => u.username)
+      .filter((u): u is string => !!u)
+  );
+
+  for (const row of rows) {
+    const base = slugify(row.name || row.email);
+    let candidate = base;
+    let suffix = 0;
+    while (taken.has(candidate)) {
+      suffix += 1;
+      candidate = `${base}${suffix}`.slice(0, 20);
+    }
+    taken.add(candidate);
+
+    await db.update(users).set({ username: candidate }).where(eq(users.id, row.id));
+    console.log(`  ${row.email} -> @${candidate}`);
+  }
+
+  console.log("Backfill complete.");
+  process.exit(0);
+}
+
+backfillUsernames().catch((err) => {
+  console.error(err);
+  process.exit(1);
+});