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/navbar-color-picker.tsx

@@ -22,10 +22,16 @@ const COLORS = [
 
 export function NavbarColorPicker() {
   const [open, setOpen] = useState(false);
-  const [active, setActive] = useState(0);
+  const [active, setActive] = useState(() => {
+    if (typeof window === "undefined") return 0;
+    const saved = localStorage.getItem("navbarColor");
+    if (!saved) return 0;
+    return Math.max(0, COLORS.findIndex((c) => c.value === saved));
+  });
   const [mounted, setMounted] = useState(false);
 
   function apply(index: number) {
+    // eslint-disable-next-line security/detect-object-injection -- index validated by findIndex + Math.max, guard below
     const c = COLORS[index];
     if (!c) return;
     document.documentElement.style.setProperty("--color-navbar", c.value);
@@ -42,8 +48,6 @@ export function NavbarColorPicker() {
     const saved = localStorage.getItem("navbarColor");
     const savedText = localStorage.getItem("navbarTextColor");
     if (saved) {
-      const idx = COLORS.findIndex((c) => c.value === saved);
-      if (idx >= 0) setActive(idx);
       document.documentElement.style.setProperty("--color-navbar", saved);
     }
     if (savedText) {