Add Custom Formula Item Templates with AI generation and wizard integration

Introduces per-company reusable NCalc2 pricing formula templates for complex
fabricated items (roof curbs, enclosures, welded frames). Templates support
two output modes — FixedRate (formula yields a dollar amount) and SurfaceAreaSqFt
(formula yields sq ft fed into the standard coating engine). Includes:

- CustomItemTemplate entity, migration (AddCustomItemTemplates), IUnitOfWork repo
- IsCustomFormulaItem / CustomItemTemplateId / FormulaFieldValuesJson flags on
  QuoteItem, JobItem, CreateQuoteItemDto; mapped in all 3 JobItemAssemblyService
  overloads and all existingItemsData JSON projections + pageMeta blocks
- ICustomFormulaAiService / CustomFormulaAiService: Claude-powered formula
  generator (natural language + optional diagram image) and NCalc2 evaluator
- CompanySettings CRUD endpoints: GetCustomItemTemplates, Create/Update/Delete,
  UploadTemplateDiagram, TemplateDiagram (blob serve), EvaluateFormula, GenerateFormulaFromAi
- Company Settings "Custom Formulas" tab + cfModal + company-settings-custom-formulas.js
- item-wizard.js: formula item type card, renderFormulaFields, wzFormulaRecalc
  (live evaluate via POST), collectStep2 formula branch, buildCardHtml / emitHiddenFields
- Formula badge in Quotes/Details and Jobs/Details; AI badge gap fixed in Jobs/Details
- Help article (CustomFormulaTemplates.cshtml), Help Index card, HelpController action,
  HelpKnowledgeBase entry; 225/225 unit tests passing

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

src/PowderCoating.Application/Services/QuotePricingAssemblyService.cs

@@ -130,6 +130,14 @@ public class QuotePricingAssemblyService : IQuotePricingAssemblyService
             return;
         }
 
+        if (itemDto.IsCustomFormulaItem && itemDto.ManualUnitPrice.HasValue)
+        {
+            item.UnitPrice = itemDto.ManualUnitPrice.Value;
+            item.TotalPrice = itemDto.ManualUnitPrice.Value * itemDto.Quantity;
+            _logger.LogInformation("Custom formula item (FixedRate) price: UnitPrice={Unit}, TotalPrice={Total}", item.UnitPrice, item.TotalPrice);
+            return;
+        }
+
         if (itemDto.CatalogItemId.HasValue)
         {
             if (itemDto.Coats != null && itemDto.Coats.Any())
@@ -243,6 +251,9 @@ public class QuotePricingAssemblyService : IQuotePricingAssemblyService
             IsAiItem = itemDto.IsAiItem,
             AiTags = itemDto.AiTags,
             AiPredictionId = itemDto.AiPredictionId,
+            IsCustomFormulaItem = itemDto.IsCustomFormulaItem,
+            CustomItemTemplateId = itemDto.CustomItemTemplateId,
+            FormulaFieldValuesJson = itemDto.FormulaFieldValuesJson,
             CompanyId = companyId,
             CreatedAt = createdAtUtc
         };