fix: replaced port character sum with a cksum hash

[CaddyDz]

Problem

port <string> summed character codes, so:

• anagrams collided (ab/ba, web-api/api-web)
• short names clustered around 49.5k–51.5k
• it forked printf once per character
• word, sum, port, … leaked into the calling shell

Changes

• port now hashes with cksum (POSIX CRC) into 49152–65535, uses local, prints usage to stderr and returns 1 without an argument
• port --check <string> warns on stderr when the port is listening locally, published by a running container, or written in a docker-compose*.yml/.env under ~/Code; it still prints the number and exits 0
• Old algorithm kept as port_legacy, because these files hardcode values it generated (left untouched):
  • FraudCentral docker-compose.yml → 50427 (fraudcentral)
  • Roboguard .env.example → 50117 (roboguard), 49921 (control)
  • Sockets docker-compose.yml → 50117 in comments only
  • xeldex docker-compose.yml → 49802 (xeldex)

Testing

name	legacy	new
fraudcentral	50427	55514
dsalim	49786	58537
crm	49474	58623
control	49921	57632
roboguard	50117	52031
crazytel-ui	50297	49804
ab / ba	49347 / 49347	56659 / 63241

• _port_check 8080 reports the local listener, the traefik container, and the compose/.env files that contain 8080
• port / port --check with no string → usage on stderr, exit 1
• No variables leak into the calling shell