perf: optimize DB layer with caching and pool tuning

- Add Redis cache wrapper (cached-db.ts) — cachedQuery + invalidate helpers
- Add cached login user lookup (auth.ts: getLoginUser) — short 15s TTL
  for brute-force protection, cache invalidation on password/rank changes
- Switch auth.ts login flow from Prisma facade to raw SQL via db.execute
  (avoids abstraction overhead for this hot path)
- Cache invalidation wired in: login password upgrade, updateUser, resetPassword
- Connection pool tuning: enableKeepAlive, namedPlaceholders,
  prepared statement cache (Node 22+), multipleStatements off (SQLi hardening)
- 0 tsc errors, 583 tests passing

src/actions/users.ts

@@ -3,6 +3,7 @@
 import crypto from "node:crypto";
 import { z } from "zod";
 import { hashPassword } from "@/lib/auth/password";
+import { invalidateLoginCache } from "@/lib/auth";
 import { PERMS } from "@/lib/permissions";
 import { prisma } from "@/lib/prisma";
 import { adminAction } from "@/lib/safe-action";
@@ -119,6 +120,7 @@ export const updateUser = adminAction(
 		}
 
 		await prisma.user.update({ where: { id }, data: userData });
+		invalidateLoginCache(targetUser.username);
 
 		if (diamonds !== undefined) {
 			await prisma.usersCurrency.upsert({
@@ -313,6 +315,7 @@ export const resetPassword = adminAction(
 			where: { id: ctx.data.userId },
 			data: { password: hashed },
 		});
+		invalidateLoginCache(target.username);
 
 		logAudit({
 			userId: ctx.session.user.id,