feat(auth): make password length configurable via env (min 5–30, max 30–128)

Add PASSWORD_MIN_LENGTH / PASSWORD_MAX_LENGTH (validated in src/env.ts) and a
shared passwordPolicy helper. The policy drives the zod schemas in register,
password reset and the admin create-user dialog, plus the live requirement
checks and strength meter in the register form.

Locale messages now interpolate the configured minimum via {min} instead of
hard-coding 12.

src/actions/password-reset.ts

@@ -6,6 +6,7 @@ import { redirect } from "next/navigation";
 import { env } from "@/env";
 import { invalidateLoginCache } from "@/lib/auth/login-core";
 import { hashPassword } from "@/lib/auth/password";
+import { passwordPolicy } from "@/lib/auth/password-policy";
 import { revokeUserCredentials } from "@/lib/auth/session-revocation";
 import { db, PasswordReset, User } from "@/lib/db";
 import { logger } from "@/lib/logger";
@@ -109,7 +110,11 @@ export async function resetPassword(formData: FormData): Promise<void> {
 	}
 
 	let error: "password" | "invalid" | "failed" | null = null;
-	if (password.length < 12) error = "password";
+	if (
+		password.length < passwordPolicy.minLength ||
+		password.length > passwordPolicy.maxLength
+	)
+		error = "password";
 
 	if (!error) {
 		try {