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/me/page.tsx

@@ -44,6 +44,13 @@ const ERROR_MESSAGES: Record<string, string> = {
   error: "Something went wrong while claiming your reward. Please try again.",
 };
 
+function getErrorMessage(error: string): string {
+  if (error === "not_enough") return ERROR_MESSAGES.not_enough;
+  if (error === "no_referrals") return ERROR_MESSAGES.no_referrals;
+  if (error === "bad_config") return ERROR_MESSAGES.bad_config;
+  return ERROR_MESSAGES.error;
+}
+
 export default async function MePage({ searchParams }: { searchParams: SearchParams }) {
   const session = await auth();
   if (!session?.user?.id) redirect("/login");
@@ -147,7 +154,7 @@ export default async function MePage({ searchParams }: { searchParams: SearchPar
         ) : null}
         {error ? (
           <div role="alert" style={feedbackStyle("error")}>
-            {ERROR_MESSAGES[error] ?? ERROR_MESSAGES.error}
+            {getErrorMessage(error)}
           </div>
         ) : null}