refactor: update Dockerfile and authentication flow for improved user experience

- Updated Dockerfile to create a cache directory for Next.js runtime, ensuring proper permissions and ownership.
- Enhanced the authentication flow by updating the magic link expiration time from 5 to 15 minutes, improving user experience and reducing login issues.
- Added user-friendly error handling for invalid or expired magic links, providing clear feedback on the login page.
- Adjusted email templates to reflect the new 15-minute validity period for magic links.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Dockerfile

@@ -69,10 +69,11 @@ COPY drizzle ./drizzle
 COPY scripts/db-goc.mjs ./scripts/db-goc.mjs
 COPY scripts/docker-entrypoint.sh ./docker-entrypoint.sh
 
-# SQLite veri dizini
+# SQLite veri dizini + Next'in runtime'da yazdığı image/fetch cache dizini
+# (.next'in geri kalanı root'ta kalır; salt-okunur olması sorun değil)
 RUN chmod +x /app/docker-entrypoint.sh && \
-    mkdir -p /app/data && \
-    chown -R nextjs:nodejs /app/data /app/seed
+    mkdir -p /app/data /app/.next/cache && \
+    chown -R nextjs:nodejs /app/data /app/seed /app/.next/cache
 
 USER nextjs