Fix NCalc case sensitivity and add formula validation

- Normalize IF/Abs/Pow/etc. to lowercase before evaluation so AI-generated
  or manually typed uppercase function names no longer cause "Function not
  found" errors
- Add NormalizeAndValidate() which normalizes then does a parse-only check
  on save — invalid formulas are rejected with a clear error before storing
- Update AI system prompt to list all functions in lowercase and explicitly
  call out case-sensitivity; add if() to the supported function list
- Add collapsible NCalc quick-reference panel in the formula editor showing
  all operators, functions (lowercase), built-in variables, and an example

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Web/Controllers/CompanySettingsController.cs

@@ -3054,6 +3054,10 @@ public class CompanySettingsController : Controller
         var fieldError = ValidateTemplateFields(dto.FieldsJson);
         if (fieldError != null) return Json(new { success = false, message = fieldError });
 
+        var (normalizedFormula, formulaError) = _formulaAiService.NormalizeAndValidate(dto.Formula);
+        if (formulaError != null) return Json(new { success = false, message = $"Formula error: {formulaError}" });
+        dto.Formula = normalizedFormula;
+
         var companyId = _tenantContext.GetCurrentCompanyId()!.Value;
         var entity = _mapper.Map<CustomItemTemplate>(dto);
         entity.CompanyId = companyId;
@@ -3076,6 +3080,10 @@ public class CompanySettingsController : Controller
         var fieldError = ValidateTemplateFields(dto.FieldsJson);
         if (fieldError != null) return Json(new { success = false, message = fieldError });
 
+        var (normalizedFormula, formulaError) = _formulaAiService.NormalizeAndValidate(dto.Formula);
+        if (formulaError != null) return Json(new { success = false, message = $"Formula error: {formulaError}" });
+        dto.Formula = normalizedFormula;
+
         var companyId = _tenantContext.GetCurrentCompanyId()!.Value;
         var entity = await _unitOfWork.CustomItemTemplates.GetByIdAsync(dto.Id);
         if (entity == null || entity.CompanyId != companyId)