Add configurable HTTP Server header for deception

Add SERVER_HEADER environment variable to customize the HTTP Server
  response header, defaulting to Apache/2.2.22 (Ubuntu). This allows the
  honeypot to masquerade as different web servers to attract attackers.

  - Add server_header field to Config dataclass
  - Override version_string() in Handler to return configured header
  - Update documentation and all deployment configs

docker-compose.yaml

@@ -20,6 +20,7 @@ services:
       - MAX_COUNTER=10
       - CANARY_TOKEN_TRIES=10
       - PROBABILITY_ERROR_CODES=0
+      - SERVER_HEADER=Apache/2.2.22 (Ubuntu)
       # Optional: Set your canary token URL
       # - CANARY_TOKEN_URL=http://canarytokens.com/api/users/YOUR_TOKEN/passwords.txt
       # Optional: Set custom dashboard path (auto-generated if not set)