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/lib/services/email.ts

@@ -1,9 +1,10 @@
 import { exec } from "child_process";
 import { writeFile, mkdir } from "fs/promises";
-import { join } from "path";
+import { resolve } from "path";
 import nodemailer, { type Transporter } from "nodemailer";
 import { Resend } from "resend";
 import { env } from "@/env";
+import { logger } from "@/lib/logger";
 
 let transporter: Transporter | null = null;
 let resend: Resend | null = null;
@@ -39,7 +40,7 @@ function sendViaSendmail(to: string, subject: string, html: string, from: string
 
     const child = exec("sendmail -t", (error) => {
       if (error) {
-        console.error("[email] sendmail failed:", error.message);
+        logger.error("Sendmail failed", { module: "email", error: error.message });
         resolve(false);
       } else {
         resolve(true);
@@ -55,16 +56,18 @@ function sendViaSendmail(to: string, subject: string, html: string, from: string
 
 async function writeToFile(to: string, subject: string, html: string, from: string): Promise<boolean> {
   try {
-    const logDir = join(process.cwd(), "storage", "logs");
+    const logDir = resolve(process.cwd(), "storage", "logs");
+    // eslint-disable-next-line security/detect-non-literal-fs-filename
     await mkdir(logDir, { recursive: true });
     const timestamp = new Date().toISOString().replace(/[:.]/g, "-");
     const filename = `email-${timestamp}.html`;
     const content = `<!-- To: ${to} | From: ${from} | Subject: ${subject} -->\n${html}`;
-    await writeFile(join(logDir, filename), content, "utf-8");
-    console.log(`[email] Written to storage/logs/${filename}`);
+    // eslint-disable-next-line security/detect-non-literal-fs-filename
+    await writeFile(resolve(logDir, filename), content, "utf-8");
+    logger.info("Email written to file", { module: "email", filename });
     return true;
   } catch (e) {
-    console.error("[email] Failed to write email to file:", (e as Error).message);
+    logger.error("Failed to write email to file", { module: "email", error: (e as Error).message });
     return false;
   }
 }
@@ -79,7 +82,7 @@ export async function sendMail(to: string, subject: string, html: string): Promi
       await r.emails.send({ from, to, subject, html });
       return true;
     } catch (e) {
-      console.error("[email] Resend failed:", (e as Error).message);
+      logger.error("Resend API failed", { module: "email", error: (e as Error).message });
     }
   }
 
@@ -89,7 +92,7 @@ export async function sendMail(to: string, subject: string, html: string): Promi
       await t.sendMail({ from, to, subject, html });
       return true;
     } catch (e) {
-      console.error("[email] SMTP failed:", (e as Error).message);
+      logger.error("SMTP failed", { module: "email", error: (e as Error).message });
     }
   }