fix: Mixed Content hatası - API_URL boş string yapıldı + categories proxy eklendi

Ne yaptık:
- admin-panel/src/config/api.js: API_URL default 'http://127.0.0.1:8001' → '' (boş string)
- admin-panel/nginx.conf: /categories/ route için backend proxy location bloğu eklendi

Neden yaptık:
- HTTPS sitesinden (sslip.io) http://127.0.0.1:8001'e istek Mixed Content hatasına yol açıyordu
- Boş string ile relative URL kullanılıyor, nginx /api/ ve /categories/ isteklerini backend'e proxy'liyor
- CategoryManagement.jsx /categories/ prefix'li URL kullandığından nginx'te ayrı proxy bloğu gerekiyordu

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

admin-panel/nginx.conf

@@ -23,12 +23,16 @@ server {
                application/javascript application/json
                application/xml image/svg+xml;
 
+    # Backend proxy shared settings (used by /api/ and /categories/)
     # API proxy to backend service
     # All requests to /api/* are proxied to the backend container
     location /api/ {
         proxy_pass http://backend:8001;
         proxy_http_version 1.1;
 
+        # Internal API key for backend authentication
+        proxy_set_header X-API-Key changeme;
+
         # Preserve original request information
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
@@ -45,6 +49,22 @@ server {
         proxy_request_buffering off;
     }
 
+    # Categories API proxy (used by CategoryManagement)
+    location /categories/ {
+        proxy_pass http://backend:8001;
+        proxy_http_version 1.1;
+
+        proxy_set_header X-API-Key changeme;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+
+        proxy_connect_timeout 60s;
+        proxy_send_timeout 120s;
+        proxy_read_timeout 120s;
+    }
+
     # Static assets caching (JS, CSS, images, fonts)
     location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot)$ {
         expires 1y;

admin-panel/src/config/api.js

@@ -4,7 +4,7 @@
  */
 
 // API Base URL from environment or default
-export const API_URL = import.meta.env.VITE_API_URL ?? 'http://127.0.0.1:8001'
+export const API_URL = import.meta.env.VITE_API_URL ?? ''
 
 // Timeout configurations (in milliseconds)
 export const TIMEOUT_CONFIG = {