feat: docker socket protocol

[Nemental]

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Description

Closes #62

This PR enhances Docker socket path handling in Newt by adding support for protocol-prefixed socket paths, such as:

• unix:///var/run/docker.sock
• tcp://localhost:2375
• http://127.0.0.1:2375
• ssh://user@host

The new parseDockerHost function extracts the protocol and address, allowing CheckSocket to validate reachability for multiple Docker API endpoints, not just local UNIX sockets.

How to test?

TCP Example with linuxserver/docker-socket-proxy

1. Add socket proxy service to your newt-compose

• Example snippet

    socket-proxy:
      image: ghcr.io/linuxserver/socket-proxy:3.2.3
      restart: unless-stopped
      environment:
        CONTAINERS: 1
        EVENTS: 1
        INFO: 1
        NETWORKS: 1
        PING: 1
        VERSION: 1
      volumes:
        - /var/run/docker.sock:/var/run/docker.sock:ro
      read_only: true
      tmpfs:
        - /run
      networks:
        - pangolin

2. Run Newt with different socket protocols

• Command Argument:

      command:
        - --docker-socket tcp://socket-proxy:2375

• Environment Variable

      environment:
        DOCKER_SOCKET: tcp://socket-proxy:2375

3. Trigger the socket check from Pangolin

• Navigate to "Resources"
• Edit a Resource
• Targets Configuration -> IP / Hostname -> View Docker Containers
• Observe logs for messages like:
  • Pangolin

    [info]: Docker socket availability for Newt id12345abc: available=true, socketPath=http://socket-proxy:2375
    

  • Newt

    DEBUG: 2025/07/30 12:41:15 Received Docker socket check request
    DEBUG: 2025/07/30 12:41:15 Docker reachable via tcp at socket-proxy:2375
    DEBUG: 2025/07/30 12:41:15 Sending message: newt/socket/status, data: map[available:true socketPath:http://socket-proxy:2375]
    INFO: 2025/07/30 12:41:15 Docker socket check response sent: available=true
    

4. Verify container listing loads successfully in the Pangolin UI.

5. Optionally, test with invalid or unreachable paths to ensure graceful error handling.