security: harden authentication (register/login)

- Username: restrict to [A-Za-z0-9_-], block reserved names (admin, mod, root, etc.),
  normalize NFC
- Password: min 12, max 128, require upper+lower+digit+special char
- Email: block disposable/temporary domains (mailinator, yopmail, etc.)
- Hashing: switch to Argon2id (memory-hard) via hash-wasm argon2id API
- Legacy hash migration: argon2/bcrypt/md5/sha1/sha256/sha512/salted/combined
  auto-upgrade to Argon2id on successful login
- Rate limits: 5/10min register, 10/5min login precheck per IP
- VPN/proxy block (configurable via /admin/vpn)
- Timing attack mitigation: dummy bcrypt hash for non-existent users
- Fixed typo in error message (R3 -> 3)
- Updated register.test.ts to match new validation rules

src/lib/auth/password.ts

@@ -1,5 +1,6 @@
 import { randomBytes } from "node:crypto";
 import {
+	argon2id,
 	argon2Verify,
 	bcrypt,
 	bcryptVerify,
@@ -11,7 +12,26 @@ import {
 
 import { env } from "@/env";
 
+/** Argon2id parameters — memory-hard, GPU-resistant. */
+const ARGON2_CONFIG = {
+	memoryCost: 19456, // ~19 MiB
+	timeCost: 2,
+	parallelism: 1,
+	outputLen: 32,
+};
+
+/** Hash new passwords with Argon2id (best practice 2024+). */
 export async function hashPassword(password: string): Promise<string> {
+	return await argon2id({
+		password,
+		salt: randomBytes(16),
+		...ARGON2_CONFIG,
+		outputType: "encoded",
+	});
+}
+
+/** Legacy bcrypt for migrating existing hashes. */
+export async function hashPasswordBcrypt(password: string): Promise<string> {
 	return await bcrypt({
 		password,
 		salt: randomBytes(16),