fix: Resolve Twig error when creating campaign conditions on custom object fields

[minholi]

Problem

When adding a campaign condition based on a custom object field value, Mautic threw a critical runtime error:

Twig\Error\RuntimeError: "Neither the property "form" nor one of the methods "form()",
"getform()"/"isform()"/"hasform()" or "__call()" exist and have public access in
class "Symfony\Component\Form\FormView"."
at ...FormBundle/Resources/views/FormTheme/FieldValueCondition/
_campaignevent_form_field_value_widget.html.twig line 4

Root cause

CampaignSubscriber::onCampaignBuild() registered the campaign condition with formTheme pointing to
@MauticForm/FormTheme/FieldValueCondition/_campaignevent_form_field_value_widget.html.twig. That template belongs to
Mautic's core FormBundle and is designed for its own lead-form "Field Value Condition" — it tries to render {{
form_row(form.form) }} (a "form" selector field), which does not exist in this plugin's
CampaignConditionFieldValueType.

Fix

1. CampaignSubscriber.php — changed formTheme to point to the plugin's own template (@CustomObjects/...) instead of
   Mautic's FormBundle template.
2. campaign_condition_field_value_widget.html.twig — the template was malformed for use as a Symfony form theme:
   - Added the required {% block _campaignevent_properties_row %} wrapper (the ID-based block Symfony looks for when
   rendering the properties row of the campaignevent form)
   - Changed {{ form_row(field) }} → {{ form_row(form.field) }} (children must be accessed via form.* inside a form
   theme block)
   - Added {{ form_widget(form.customObjectId) }} to ensure the hidden field is included in the form submission
   - Removed stray PHP tags () that had no effect in a Twig file

[escopecz]

The code changes make sense 👍