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/navigation.tsx

@@ -1,5 +1,6 @@
 import { getTranslations } from "next-intl/server";
 import Link from "next/link";
+import Image from "next/image";
 import { auth } from "@/lib/auth";
 import { LanguageSwitcher } from "@/components/language-switcher";
 import { MobileNav } from "@/components/mobile-nav";
@@ -19,14 +20,14 @@ export async function Navigation() {
       
         <div className="flex items-center gap-x-1 md:gap-x-1 flex-1 md:flex-none">
           <Link href="/" className="nav-item shrink-0">
-            <img src="/assets/images/icons/navigation/me.png" alt="" className="w-5 h-5 mr-1.5" />
+            <Image src="/assets/images/icons/navigation/me.png" alt="" width={20} height={20} className="mr-1.5" />
             <span>{t("home")}</span>
           </Link>
         </div>
 
         <MobileNav menuLabel={t("openMenu") || "Open menu"} closeLabel={t("closeMenu") || "Close menu"}>
           <Link href="/" className="nav-item md:hidden" role="menuitem">
-            <img src="/assets/images/icons/navigation/me.png" alt="" className="w-5 h-5 mr-1.5" />
+            <Image src="/assets/images/icons/navigation/me.png" alt="" width={20} height={20} className="mr-1.5" />
             {t("home")}
           </Link>
 
@@ -45,12 +46,12 @@ export async function Navigation() {
           </NavDropdown>
 
           <Link href="/leaderboard" className="nav-item" role="menuitem">
-            <img src="/assets/images/icons/navigation/leaderboards.png" alt="" className="w-5 h-5 mr-1.5" />
+            <Image src="/assets/images/icons/navigation/leaderboards.png" alt="" width={20} height={20} className="mr-1.5" />
             {t("leaderboards")}
           </Link>
 
           <Link href="/radio" className="nav-item" role="menuitem">
-            <img src="/assets/images/icons/navigation/bb.png" alt="" className="w-5 h-5 mr-1.5" />
+            <Image src="/assets/images/icons/navigation/bb.png" alt="" width={20} height={20} className="mr-1.5" />
             {t("radio")}
           </Link>
 
@@ -66,11 +67,11 @@ export async function Navigation() {
           {session?.user ? (
             <>
               <Link href="/friends" className="nav-item">
-                <img src="/assets/images/icons/navigation/goody.png" alt="" className="w-5 h-5 mr-1.5" />
+                <Image src="/assets/images/icons/navigation/goody.png" alt="" width={20} height={20} className="mr-1.5" />
                 {t("friends")}
               </Link>
               <Link href="/messages" className="nav-item">
-                <img src="/assets/images/icons/navigation/bb.png" alt="" className="w-5 h-5 mr-1.5" />
+                <Image src="/assets/images/icons/navigation/bb.png" alt="" width={20} height={20} className="mr-1.5" />
                 {t("messages")}
               </Link>
             </>
@@ -78,7 +79,7 @@ export async function Navigation() {
 
           {isStaff ? (
             <Link href="/admin" className="nav-item">
-              <img src="/assets/images/icons/navigation/home.png" alt="" className="w-5 h-5 mr-1.5" />
+              <Image src="/assets/images/icons/navigation/home.png" alt="" width={20} height={20} className="mr-1.5" />
               {t("admin")}
             </Link>
           ) : null}