In success case, CGI scripts should return 0, not 1.

[0-wiz-0]

Issue

When running the included Python server for collectd-web, there are lots of errors like this in the log (i.e. on stdout);

127.0.0.1 - - [06/Dec/2025 22:02:29] CGI script exit code 1

These are not needed or wanted, since in all three cases the code was executed successfully.

Description

Make the CGI script return 0 instead of 1, which is interpreted as an error.

Checklist

• I have read the contributing guidelines.

Yes - and noticed that the link is broken and should be https://github.com/httpdss/collectd-web/blob/master/.github/CONTRIBUTING.md instead.

• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have updated the documentation accordingly.

Screenshots (if applicable)

Additional Comments

[Copilot]

Pull request overview

This PR fixes incorrect exit codes in three CGI script functions. The functions were returning 1 (indicating error) in success cases, which caused spurious error log messages when using the Python server.

Key Changes:

• Changed return values from 1 to 0 for successful execution in CGI handler functions
• Affects three JSON response functions: list_hosts_json, action_show_host_json, and action_show_plugin_json

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