feat: migrate application port from 3000 to 4001 and fix circular dependencies

- Change default port to 4001 across all configuration files (server.js, docker-compose.yml, .env, Dockerfile)
- Update frontend API URL to use new port 4001
- Fix circular dependency issues in route files by using process.env.SERVER_DIR instead of importing from server.js
- Apply to all routes: auth.js, backup.js, logs.js, players.js, rcon.js, server.js, whitelist.js
- Fix environment variable loading in start.sh to properly handle paths with spaces
- Quote SERVER_DIR path in .env to preserve spaces in directory paths
- Update all documentation references from port 3000 to 4001 (README, QUICKSTART, CONFIGURATION, INDEX)
- Remove debug console.log statements from auth.js
- Remove test utility file test-ops.js

Fixes: Port conflict issues, circular dependency warnings, environment variable parsing

backend/data/users.json

@@ -0,0 +1,9 @@
+[
+  {
+    "id": "1770229357567",
+    "username": "admin",
+    "mcUsername": "anakine22",
+    "password": "$2a$10$Ie5mXaPcz.zrQ.bPFTpGbuWJ3rqPCxU8lGlcHvnJzxigkIufSaG7K",
+    "createdAt": "2026-02-04T18:22:37.567Z"
+  }
+]