Replace Basic Auth with login page, add HTTP redirect and log viewer

- Session-based login page instead of HTTP Basic Auth
- /ca.crt download works without login for easy device access
- HTTP port (default 8080) redirects to HTTPS automatically
- Nginx access/error log viewer in WebUI
- API still supports Basic Auth for curl/scripts
- Logout button and log navigation in header

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.env.example

@@ -13,5 +13,6 @@ CERT_DAYS=36500
 
 # --- WebUI-Einstellungen ---
 WEBUI_PORT=8443
+WEBUI_PORT_HTTP=8080
 WEBUI_USERNAME=admin
 WEBUI_PASSWORD=admin123