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/app/radio/contests/[id]/page.tsx

@@ -16,7 +16,7 @@ export default async function RadioContestDetailPage({
   params: Promise<{ id: string }>;
 }) {
   const { id } = await params;
-  const t = await getTranslations("pages.radioContests");
+  await getTranslations("pages.radioContests");
 
   let contestId: bigint;
   try {
@@ -26,7 +26,7 @@ export default async function RadioContestDetailPage({
   }
 
   const contest = await prisma.radioContests
-    .findUnique({ where: { id: contestId! } })
+    .findUnique({ where: { id: contestId } })
     .catch(() => null);
 
   if (!contest) notFound();

src/app/radio/giveaways/[id]/page.tsx

@@ -16,7 +16,7 @@ export default async function RadioGiveawayDetailPage({
   params: Promise<{ id: string }>;
 }) {
   const { id } = await params;
-  const t = await getTranslations("pages.radioGiveaways");
+  await getTranslations("pages.radioGiveaways");
 
   let giveawayId: bigint;
   try {
@@ -26,7 +26,7 @@ export default async function RadioGiveawayDetailPage({
   }
 
   const giveaway = await prisma.radioGiveaways
-    .findUnique({ where: { id: giveawayId! } })
+    .findUnique({ where: { id: giveawayId } })
     .catch(() => null);
 
   if (!giveaway) notFound();

src/app/radio/layout.tsx

@@ -10,8 +10,6 @@ const RADIO_SIDEBAR_LINKS = [
   { key: "leaderboard", href: "/radio/leaderboard", icon: "🏆" },
 ] as const;
 
-const SIDEBAR_KEYS = RADIO_SIDEBAR_LINKS.map((l) => l.key);
-
 export default async function RadioLayout({ children }: { children: ReactNode }) {
   const t = await getTranslations("pages.radio");
 

src/app/radio/requests/page.tsx

@@ -10,12 +10,6 @@ function formatDate(d: Date | null | undefined): string {
   return d ? d.toISOString().slice(0, 16).replace("T", " ") : "";
 }
 
-const DAYS = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"] as const;
-
-function formatDay(d: Date): string {
-  return DAYS[d.getUTCDay()] ?? "";
-}
-
 export default async function RadioRequestsPage() {
   const t = await getTranslations("pages.radioRequests");
   const genericT = await getTranslations("pages.radio");