Features: 1) Added arith template tags for sub and neg operations to support arithmetic in templates;

Fixes: 1) Replaced `add:-X` with `sub:X` in template logic for consistent arithmetic;

Extra: 1) Added `arith` to template load context; 2) Introduced `_to_float` helper for safe type conversion; 3) Used `suppress` to handle invalid conversions gracefully.

engine/core/templates/admin/index.html

@@ -1,5 +1,5 @@
 {% extends 'admin/base.html' %}
-{% load i18n unfold static %}
+{% load i18n unfold static arith %}
 
 {% block title %}
     {% if subtitle %}
@@ -68,7 +68,7 @@
                             {% endcomponent %}
                             {% if total and total > 0 %}
                                 {% with net=revenue_net_30|default:0 %}
-                                    {% with tax_amt=gross|add:-net %}
+                                    {% with tax_amt=gross|sub:net %}
                                         {% with returns_capped=returns %}
                                             {% if returns > gross %}
                                                 {% with returns_capped=gross %}{% endwith %}
@@ -77,7 +77,7 @@
                                                 {% if tax_amt_pos < 0 %}
                                                     {% with tax_amt_pos=0 %}{% endwith %}
                                                 {% endif %}
-                                                {% with net_for_pie=gross|add:-tax_amt_pos|add:-returns_capped %}
+                                                {% with net_for_pie=gross|sub:tax_amt_pos|sub:returns_capped %}
                                                     {% if net_for_pie < 0 %}
                                                         {% with net_for_pie=0 %}{% endwith %}
                                                     {% endif %}

engine/core/templatetags/arith.py

@@ -0,0 +1,22 @@
+from contextlib import suppress
+
+from django import template
+
+register = template.Library()
+
+
+def _to_float(val: object) -> float:
+    conv: float = 0.0
+    with suppress(Exception):
+        return float(val)  # type: ignore [arg-type]
+    return conv
+
+
+@register.filter(name="sub")
+def sub(value: object, arg: object) -> float:
+    return _to_float(value) - _to_float(arg)
+
+
+@register.filter(name="neg")
+def neg(value: object) -> float:
+    return -_to_float(value)