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/draw-badge/page.tsx

@@ -29,6 +29,12 @@ const ERROR_NOTE: Record<string, string> = {
   fail: "Something went wrong. Please try again.",
 };
 
+function getErrorNote(error: string): string {
+  if (error === "invalid") return ERROR_NOTE.invalid;
+  if (error === "credits") return ERROR_NOTE.credits;
+  return ERROR_NOTE.fail;
+}
+
 export default async function DrawBadgePage({
   searchParams,
 }: {
@@ -104,7 +110,7 @@ export default async function DrawBadgePage({
             role="alert"
             style={{ margin: "1rem 0 0", fontWeight: 700, color: "var(--color-danger)" }}
           >
-            {ERROR_NOTE[error] ?? ERROR_NOTE.fail}
+            {getErrorNote(error)}
           </p>
         ) : null}
       </ContentCard>