Added liking and security measures

.env.example

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+# Copy to .env and fill in real values.
+# NEVER commit .env. Use strong, unique secrets in production.
+
+PORT=3000
+
+# PostgreSQL
+DB_HOST=localhost
+DB_PORT=5432
+DB_USER=replace_me
+DB_PWD=replace_with_strong_password
+DB_DATABASE=file_cabinet
+
+# Neo4j
+GRAPH_DB_USER=replace_me
+GRAPH_DB_PWD=replace_with_strong_password
+GRAPH_DB_URI=neo4j://localhost:7687
+GRAPH_DB_NAME=neo4j
+
+# CORS allowlist (comma-separated). Empty disables all cross-origin requests.
+CORS_ALLOWED_ORIGINS=http://localhost:5173
+
+# At least 32 random characters. Generate with: openssl rand -base64 48
+JWT_SECRET=replace_with_long_random_string
+JWT_EXPIRES_IN=86400
+
+# Uploads
+UPLOAD_DIR=./uploads
+MAX_UPLOAD_SIZE_BYTES=5242880