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/public/logo-generator.tsx

@@ -42,8 +42,6 @@ export default function LogoGenerator() {
   // Load font and render preview
   useEffect(() => {
     let cancelled = false;
-    setFontLoaded(false);
-    setFontError(false);
 
     getFontInfo(styleName)
       .then((info) => {
@@ -104,7 +102,8 @@ export default function LogoGenerator() {
     try {
       const JSZip = (await import("jszip")).default;
       const zip = new JSZip();
-      const folder = zip.folder(safeText.replace(/[^a-z0-9]+/gi, "_") || "logo")!;
+      const folder = zip.folder(safeText.replace(/[^a-z0-9]+/gi, "_") || "logo");
+      if (!folder) throw new Error("Failed to create zip folder");
       let fail = 0;
 
       for (const font of allFonts) {