Remove AddTrailingSlash middleware that broke admin panel

The AddTrailingSlash() Pre middleware was redirecting requests like
/api/admin/users to /api/admin/users/, but admin routes were registered
without trailing slashes, causing routes to not match (404/401 errors).

Mobile API routes already have trailing slashes explicitly defined,
so this middleware was unnecessary and caused conflicts.

Also fix APNS_AUTH_KEY_PATH to use environment variable.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker-compose.yml

@@ -77,7 +77,7 @@ services:
       EMAIL_USE_TLS: "${EMAIL_USE_TLS:-true}"
 
       # Push Notifications (Direct APNs/FCM - no Gorush)
-      APNS_AUTH_KEY_PATH: "/certs/apns_key.p8"
+      APNS_AUTH_KEY_PATH: ${APNS_AUTH_KEY_PATH}
       APNS_AUTH_KEY_ID: ${APNS_AUTH_KEY_ID}
       APNS_TEAM_ID: ${APNS_TEAM_ID}
       APNS_TOPIC: ${APNS_TOPIC:-com.example.casera}