Security hardening, code quality, and ESLint setup

- Remove production DB dump (db_backup_*.sql) and update.log from git tracking
- Add DB backups to .gitignore
- Replace all console.log/console.error with structured logger module
- Translate Dutch error messages to English (link-discord.ts)
- Remove dead code blocks (register-form.tsx false && pattern)
- Add ESLint flat config with TypeScript, React, Next.js, jsx-a11y, and security plugins
- Add Prettier config
- Add eslint-plugin-security for security-aware linting
- Fix all 119+ ESLint warnings across the codebase:
  - Resolve security/detect-object-injection with safe access patterns
  - Resolve security/detect-non-literal-fs-filename with path traversal validation
  - Replace <img> with next/image <Image> component
  - Remove unused variables and imports
  - Replace non-null assertions with proper type guards
  - Replace <a> with <Link> for internal navigation
  - Use next/script Script component for external scripts
- Fix setState-in-useEffect anti-patterns (navbar-color-picker, logo-generator, theme-switcher)
- Add lint and format scripts to package.json

All checks: typecheck ✓, tests 58/58 ✓, lint 0 errors 0 warnings ✓

src/actions/draw-badge.ts

@@ -5,7 +5,6 @@ import { redirect } from "next/navigation";
 import { auth } from "@/lib/auth";
 import { prisma } from "@/lib/prisma";
 import { rcon } from "@/lib/services/rcon";
-import { sendCurrency } from "@/lib/services/send-currency";
 import { siteSettings } from "@/lib/services/site-settings";
 
 /**
@@ -53,7 +52,7 @@ export async function buyBadge(formData: FormData): Promise<void> {
   const rawId = String(formData.get("id") ?? "").trim();
   if (!/^\d+$/.test(rawId)) redirect("/draw-badge?error=invalid");
 
-  let outcome: "bought" | "invalid" | "credits" | "fail" = "fail";
+  let outcome: "bought" | "invalid" | "credits" | "fail";
   let boughtCode = "";
 
   try {