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/api/admin/users/actions/route.ts

@@ -5,11 +5,11 @@ import { requireStaff } from "@/lib/admin/guard";
 import { prisma } from "@/lib/prisma";
 import { rcon } from "@/lib/services/rcon";
 import { logStaffActivity } from "@/lib/services/staff-activity";
-import { CurrencyType } from "@/lib/services/currency";
+import { logger } from "@/lib/logger";
 
 const giveCurrency = async ({
-  rconClient,
-  db,
+  rconClient: _rconClient,
+  db: _db,
   userId,
   type,
   amount,
@@ -158,7 +158,7 @@ export async function POST(request: Request) {
       { status: 400 }
     );
   } catch (error) {
-    console.error("Admin users actions error:", error);
+    logger.error("Admin users actions error", { module: "admin/users/actions", error: String(error) });
     return NextResponse.json(
       { success: false, message: "Internal server error" },
       { status: 500 }