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/components/auth/register-form.tsx

@@ -2,6 +2,7 @@
 
 import { useActionState, useState } from "react";
 import Link from "next/link";
+import Image from "next/image";
 import { useTranslations } from "next-intl";
 import { register } from "@/actions/register";
 
@@ -38,7 +39,7 @@ export function RegisterForm({
             <div className="absolute inset-0 rounded-full overflow-hidden" style={{ zIndex: -1 }}>
               <div className="w-full h-full" style={{ background: "black", filter: "blur(8px)", transform: "scale(1.2)", opacity: 0.6 }} />
             </div>
-            <img src="/assets/images/FrankwithBag.gif" className="w-full h-full" style={{ objectFit: "contain", objectPosition: "center" }} />
+            <Image src="/assets/images/FrankwithBag.gif" alt="" fill className="!static" style={{ objectFit: "contain", objectPosition: "center", width: "100%", height: "100%" }} />
           </div>
         </div>
       </div>
@@ -203,18 +204,6 @@ export function RegisterForm({
           {isPending ? t("creatingAccount") : t("createAccount")}
         </button>
 
-        {/* Social Login - optional */}
-        {false && (
-          <div className="pt-4 border-t" style={{ borderColor: "color-mix(in srgb, var(--color-text-muted) 15%, transparent)" }}>
-            <p className="text-center text-sm mb-3" style={{ color: "var(--color-text-muted)" }}>
-              Or register with
-            </p>
-            <div className="flex flex-col gap-2">
-              {/* Google, Discord, GitHub buttons would go here */}
-            </div>
-          </div>
-        )}
-
         <div className="text-center">
           <Link href="/login" className="text-sm font-semibold hover:underline" style={{ color: "var(--color-primary)" }}>
             {t("alreadyHaveAccount")}