Fix checkbox config values always returning "1"

[jaycollett]

Summary

Fixes a bug where checkbox-type config options (like ignore_tls) always save as "1" regardless of whether the checkbox is checked or unchecked.

Problem

The JavaScript code collecting config values uses $(this).val() for all form elements. For checkboxes, .val() returns the value attribute (typically "1") rather than reflecting the checked state. This means unchecking a boolean config option has no effect - it still saves as "1".

Solution

Check if the element is a checkbox and use the :checked state to determine the value:

if ($(this).is(":checkbox")) {
  data[config] = $(this).is(":checked") ? "1" : "0";
} else {
  data[config] = $(this).val();
}

Test plan

• Add an enhanced app with a boolean config option (e.g., Pi-hole with ignore_tls)
• Enable the checkbox, test config - verify it saves as "1"
• Disable the checkbox, test config - verify it now saves as "0"

Fixes linuxserver/Heimdall-Apps#782