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/actions/link-discord.ts

@@ -2,33 +2,32 @@
 
 import { prisma } from "@/lib/prisma";
 import { auth } from "@/lib/auth";
+import { logger } from "@/lib/logger";
 
 export async function linkDiscordId(discordId: string): Promise<string | null> {
   const session = await auth();
-  if (!session?.user?.id) return "Niet ingelogd";
+  if (!session?.user?.id) return "Not logged in";
 
   const userId = Number(session.user.id);
   if (!discordId || !/^\d{17,20}$/.test(discordId.trim())) {
-    return "Ongeldig Discord ID";
+    return "Invalid Discord ID format";
   }
 
   const discordIdClean = discordId.trim();
 
-  // Check if this Discord ID is already linked to another account.
   try {
     const existing = await prisma.socialAccounts.findUnique({
       where: { provider_providerId: { provider: "discord", providerId: discordIdClean } },
       select: { userId: true },
     });
     if (existing && Number(existing.userId) !== userId) {
-      return "Dit Discord ID is al gekoppeld aan een ander account";
+      return "This Discord ID is already linked to another account";
     }
   } catch {
-    return "Fout bij controleren Discord ID";
+    return "Failed to check Discord ID";
   }
 
   try {
-    // Upsert: create or update the social_accounts entry.
     await prisma.socialAccounts.upsert({
       where: { provider_providerId: { provider: "discord", providerId: discordIdClean } },
       create: {
@@ -41,15 +40,14 @@ export async function linkDiscordId(discordId: string): Promise<string | null> {
       update: { userId: BigInt(userId), updatedAt: new Date() },
     });
 
-    // Mark user as verified.
     await prisma.user.update({
       where: { id: userId },
       data: { mailVerified: "1" },
     });
 
-    return null; // success
+    return null;
   } catch (e) {
-    console.error("[link-discord] Failed:", (e as Error).message);
-    return "Fout bij koppelen van Discord account";
+    logger.error("Failed to link Discord account", { module: "link-discord", error: (e as Error).message });
+    return "Failed to link Discord account";
   }
 }